Windows 7 will always boot to drive letter C: in multiboot configurations.

you either need to use multiple hard drives, or create multiple partitions on the existing hard drive. operating systems should be installed in order from oldest to newest, and, if you do it that way, and create your partitions ahead of time (can be done in computer management/disk management shrink disk/create new partition commands in windows vista or later), the bootloaders will automatically add the previous operating system to the boot list of the new operating system

I would suggest you to follow these methods.

Method 1
Last known good configuration
It's a Windows startup option that uses the most recent system settings that worked correctly. Every time you turn your computer off and Windows shuts down successfully, important system settings are saved in the registry. If a problem occurs, you can restart your computer using those settings. For example, if a new driver for your video card is causing problems, or an incorrect registry setting is preventing Windows from starting correctly, you can restart your computer using Last Known Good Configuration.
1.Remove all floppy disks, CDs, and DVDs from your computer, and then restart your computer by clicking the Start button, clicking the arrow next to the Shut Down button, and then clicking Restart.
2.Do one of the following:
·If your computer has a single operating system installed, press and hold the F8 key as your computer restarts. You need to press F8 before the Windows logo appears. If the Windows logo appears, you'll need to try again by shutting down and restarting your computer.
·If your computer has more than one operating system, use the arrow keys to highlight the operating system you want to start, and then press F8.
3.On the Advanced Boot Options screen, use the arrow keys to highlight Last Known Good Configuration (advanced), and then press Enter.
4.If your computer has more than one operating system installed, use the arrow keys to highlight the operating system that you want to start by using Last Known Good Configuration, and then press Enter. Windows will then resume starting normally.
Method 2
Chkdsk (Chkdsk.exe) is a command-line tool that checks volumes for problems. The tool then tries to repair any that it finds.
1.Boot from the DVD
2. Select the Language
3. Click on "Repair your Computer" on the Install now screen
4. Click next on the System Recovery Options screen
5. Click on Command prompt.
6. Type the command chkdsk and press enter
Method 3
Offline system restore.
1. Boot from the DVD
2. Select the Language
3. Click on "Repair your Computer" on the Install now screen
4. Click next on the System Recovery Options screen
5. Click on System Restore.
6. Choose the date to which you want to restore
Refer this link for more information.
A Windows Vista-based computer that has a Windows Recovery Environment (Windows RE) partition is not successfully restored by using Windows Complete PC Backup and Restore
http://support.microsoft.com/kb/946010
Good luck,

When installing different versions of Windows, you must start with the oldest system first.

1. Booting from XP disc, create 2 partitions before installing and install XP to one of them.
2. After XP is complete, install W7 to second partition and after it is complete you will be given the OS System Boot choice at Start Up.

Regards,

Selk

i use nero 6 but am willing to try other software if it'll work...

The Boot Configuration Data (BCD) store contains boot configuration parameters and controls how the operating system is started in Microsoft®Windows Vista.
Remove Windows Vista From Dual Boot System Windows Vista works slightly different from earlier versions of Windows when installed on a dual boot system, in that it has a completely different boot loader.
When Windows Vista is first installed as a dual boot operating system a new boot folder is added to the root directory of your PC. This is a hidden file and therefore is not noticed. When you boot your PC a menu appears with the following options:

• Earlier versions of Windows
• Windows Vista

Clicking the Windows Vista option will boot the PC into Windows Vista. If, however, you select the earlier versions of Windows option, another menu will appear from which you can choose Windows XP or whatever earlier version - Windows 2000 or Windows 2003 server - you installed first.
Because of this new boot loader it is not as easy to remove Vista from a dual boot system scenario. Simply deleting the Vista partition will, of course, remove Windows Vista, but, unfortunately, it will not remove the Windows Vista boot loader. For this reason, if you simply delete the Windows Vista partition, on rebooting your machine you will not automatically boot into Windows XP (or an earlier version). Instead you will once again be presented with a menu from which you have to choose which operating system you wish to boot to.
Obviously, once you have removed the boot loader and rebooted the Vista operating system will still be on the partition you originally installed it on. To remove Vista completely you will need to Delete the partition that Windows Vista was installed upon.
To remove this menu, or more to the point, the boot loader, proceed as follows:
1/ Boot the PC to Windows Vista
2/ Ensure you are logged onto the Internet and then download the freeware boot loader utility VistaBootPro (www.vistabootpro.org)
3/ Once you have downloaded VistaBootPro, install it on your machine
4/ During Install VistaBootPro will install an icon on your desktop
5/ Locate the VistaBootPro icon and Right Click on it. Then, from the drop down menu, Click on the Run As Administrator option
6/ User Account Control (UAC) will pop up and ask for permission to run the program
7/ After you have given UAC permission - you must be the administrator or have administrator privileges - VistaBootPro will run.
8/ Once VistaBootPro opens, Click on the Bootloader tab
9/ In the Bootloader Maintenance section, Click on the Radio button next to the option marked 'Uninstall the Vista Bootloader (Used to restore Legacy OS) option' and then Click the Apply button
10/ Finally Reboot your PC
11/ On rebooting your machine you will boot directly into Windows XP (or an earlier operating system). No menu will appear.
12/ All that is left to do now is to delete the partition which originally contained Windows Vista. (Assuming you wish to remove the Vista partition from your hard drive).