Have you downloaded and installed the Vista driver? Go to:
Lexmark Downloads
Enter your model number in the "Search by Model" box. Click on the gray X5270 in the box that appears.
If the tab at the bottom doesn't say "Vista", select it from the Operating System drop-down menu. This is the file you need to download:
cjr5200EN.exe
Click on the "Download Now" button. Confirm the security prompts. When it asks if you want to Install or Save the file, Save it to your Desktop.
After the download, make sure you remove all of the previous printer software already installed. Also delete the printer from your Printers control panel selection.
Follow the Setup procedure found here:
X5270 Setup
Remember to turn your printer ON. Connect the USB cable. (If you get a Found New Hardware box, Cancel it out by clicking the "X" in the upper right corner.
Then instead of inserting a CD, simply run (double-click) the file on your desktop to install the software.