I know this is an older forum post and maybe you already found a workable solution... or even if your lucky ...stepped up to a newer PC.
If your still looking for a good solution maybe this can help.
I just recently did some special things to my E310 that literally took this thing to a new era of performance for what it is... probably about the best you can do on it.
I already wrote a book on all this that can be found on this post here ---> http://www.tomshardware.com/forum/386135-33-video-card-dell-dimension-e310#10694172
I am very very happy with the performance increase that I get running Win7 x64 on my Dell E310 and E510. I for one wouldn't go back or even to 32-bit Win7 for anything.
Even the fact you don't have to track down all the drivers from Dell with Win7 anymore. I didn't have the problem with the video drivers you were having as I had a Radeon HD 4670 PCIe x16 2.0 512MB GPU installed at the time of my Win7 install... and yes I as well as every other Dell E310 owner only have a PCIe x1 slot on my mobo. But if you already jumped to my other forum post you probably know why already.
Hope you get some use from the info. It all went pretty smoothly actually for me and I was just winging it.