Your motherboard has a PCI-E x16 slot, so the card you're buying will fit perfectly. Don't sweat it; any PCI-E card works on your board regardless of it being version 1.0. You might lose a tiny fraction of performance, but don't let that bother you. Your real bottlenecks are the processor—which is too weak for modern cards—and especially the power supply.
The bigger issue is that there isn't anything better than the HD5670 for $167. If you want something for AutoCAD, a GTS450 would be a much better fit and costs about $227. That card has CUDA cores to speed up graphic processing, which the ATI lacks, not to mention it's significantly more powerful for gaming.
http://www.techcrunch.com Plus, factor in shipping to Indianapolis or just grab it directly from the Links site here:
Good catch on the memory. Look for DDR5; that’s why the ones with DDR3 or heaven forbid DDR2 are cheaper. They try to bait you with those massive 1GB or 2GB numbers, but it's just a gimmick.
If you absolutely can't scrape together enough for the GTS450, then the HD5670 is your only option. Otherwise, you simply don't have enough cash for serious gaming or work.
But since you're running that off-brand power supply, watch your wattage. The GTS450 pulls about 100W, while the HD5670 pulls around 60W.
- give them a call. It says it's new and unused. If everything checks out and it has a warranty, that would be your best bet if you can afford to add $67... there's no reason to fear used gear.
But seriously, get a new power supply soon if you decide to go with Nvidia.