My wide zoom lens for my D200 will not auto focus..

Your lens might need to be recalibrated. Try sending it to PhotoTech Repair Service in NYC. They are Nikon authorized, and can do the repair under warranty if you still have it. Also if you join they're facebook page, they will give you a 10% discount.
Here is the facebook page link, it has everything you need to send it in.
http://www.facebook.com/pages/New-York-NY/PhotoTech-Repair-Service-Inc/102527215194

Make sure your AF-switch on your camera and your lens are both turned on.

My lens is also doing that same thing... and I just posted pretty much the exact thing you said...Mine squeaks and goes in and out really fast.. I do know that you can put the camera on manual mode and focus manually on mine, but would like to have the auto focus sometimes too. If I dont get an answer soon, I may send it in... I believe its a motor problem in the lens....

Maje sure you lens it not set to manual focus and that the lens is mounted correctly. Also - FWIW - shoot with a fast shutter speed (1/250 or better) to avoid blur.

You have named several excellent digital SLR cameras aimed at the top end of the amateur/semi professional market.
I have the Nikon D200 and have been very pleased with it.
As stated by JCDill, you must really decide what you want and can afford. The camera body you choose will commit you down one path or another. For example, if you choose Canon, only Canon or OEM (Other Equipment Manufacturers) such as Sigma lenses will fit your camera body. Canon have a good reputation for their auto-focus, while Nikon make lenses that are the envy of others.
If this is your first digital SLR then you might be best buying an entry level body with a multi-purpose zoom lens such as the Nikon D40. There is a lot to learn.
If you are converting from film SLR and already have a set of lenses, then the cameras you mentioned will probably be able to use your existing lenses (but this is less so with Canon than Nikon). I was ecstatic to disover that my old Nikon 500mm mirror lens works in manual mode (with metering displayed) on my Nikon D200 but would not work properly on my Nikon D70.
I hope this helps.

I will try to help you, but please understand that my experience is with Nikon film cameras. Assuming that the D60 works in a manner similar to a Nikon 35 mm body and that Sigma macro lens work like Nikon macro lens, you should be able to determine the usable subject to lens distance by experimentation. First, make sure the lens is in the macro mode. To do this you must set the auto-focus mode control to the manual focus mode (see your manual). On Nikon lenses, you must first set the focus ring to infinity, then move slider switch, which has two positions marked; "normal" and "macro., to the macro position. You should now be able to rotate the focus ring to the macro range. Use the zoom ring to zoom in and out and focus with the focus ring. The the range over which the lens to subject to lens distance will yield an in focus image will be rather limited and in the range of an inch or so to 6 or 8 inches.

Try cleaning your sensor manualy.

in any case where the lens makes a grinding noise, something is in the channel and causing the lens to not extend all the way... you will need to send to a repair shop

If it's any consolation, I have the same setup and the same problem. I'm now at the point where I'm probably going to have to return the lens as faulty, but there are a few things it could be on yours which you might want to check.

Have you got the D200 set to auto-focus? The selector (on the front of the camera, on the lower left) should be in the S position (as opposed to C or M).

Have you got the lens set to auto-focus? It should be in the M/A position, rather than M.

Have you tried cleaning the contacts? Pop the lens off and give the contacts a clean with the appropriate equipment. Dust on the contacts could be causing a problem.

Failing that, have you tried turning the camera on and off a few times?

I've obviously tried all the above on mine, and now suspect I've got a faulty lens that needs fixing ... which really sucks! Good luck with it, let me know if you get it working.

Dan

HI, are you sure that there is no conversion lens setting activated in the setup menu? It sounds like that to me. These modes limit the ranges. I hope it will help, otherwise you will have to bring it back.