Yes, you can get a PC without Vista -especially is you go with one of the real cheap boxes. If you want to go with Dell, or someone like that, keep an eye on www.bensbargains.net - there will often be great coupon deals for PCs from Dell. I usually buy from Dell, but I have also gotten very inexpensive PCs from pcconnection.com, buy.com and tigerdirect.com.
For antivirus, I am a huge fan of AVG by Grisoft - both Norton and Mcafee and total resource hogs and I find them very intrusive. AVG has a free personal version, and I now use the very inexpensive SOHO version to protect all of my PCs. I've never had a problem with it.
You'll probably get a nice long life out of your next PC if you go for something that can take 1 gig of RAM or more, and has a big hard drive. If you buy an inexpensive box with 512 meg RAM, see if you can get all that ram on one card in one slot, then use a site like 4allmemory.com or any of the other memory sites to get a compatible card for the other slot. It is often cheaper to buy the PC with less ram, and then buy more RAM from another site.
Good luck!
Keep calm and carry on...