Larry, DO NOT BUY A 2000 AUDI S4!!!!!! I've already researched the crap out of it, and even the owners say not to do so. Let me find you info and post why...
On turbo failures (see second link) " There are failures unfortunately, and when they do fail it's talked about very vocally because the price is extreme: $4-5k to have them replaced. "
http://www.audiforums.com/m_279895/tm.htm But if you're serious READ THIS ONE! >>>>>>>>
http://www.audiworld.com/tech/misc45.shtml
If you're going to get an Audi, I'd recommend an A4 Quattro 1.8t. Some people like to say the 1.8t is slow, but I find it damn fun to drive. Plus, they have a nice ecu upgrade out for it:
http://www.goapr.com/Audi/products/index.html
If you really want an S4, don't let it be your daily driver.