hum, totally missed this thread. Anyhow, Both the Rebel XT and XTi are great camera's. You can get the XT for about 400-500 new body only, and the XTi about 650-750 new body only. You can get some deals on them like 550 for a new XTi body only. I have the XTi and the 30D and I use my 30D almost exclusively compared to the XTi and it's 2MP less than the rebel.
It depends on what your wife is gonna be using it for. If she wants a simple, easy camera to tote around, then look for a prosumer camera from sony or canon. If she wants to be very creative and take pictures of high quality, then SLR is the way to go.
Since the 30D was just recently discontinued, you might just end up picking one of them up for "cheap", which is about $1000 new. You can go like me and buy used or refurbished for $800ish. 20D's are older bodies but same camera, same features, just a small LCD on the back and they usually sell for $500-600 used.
8MP is more than enough a don't get the idea that more MP = better camera, it doesn't. Joe Wierzbicki still uses his original 1D which is only 4MP, but still pumps out pro quality pictures. More MP means you can play around more with cropping, which is a valuable asset when you are starting to learn specially if you can't frame worth a damn when shooting.