Should I upgrade my MOBO or just buy a new video card?

[Bhstickman]

I'll start with my specs:
AMD Athlon XP 3100+ 2.2 ghz rated at 3.1 ghz
1 gb of PC2700 Ram
ATI Radeon 9200SE

With newer games becoming available on the market, they require better and better computers. My video card is pretty much extinct, as it does not support DX 9, Pixel Shader 2.0, and overall is a very slow card. I would really like to upgrade my computer in order to play newer games such as Oblivion, F.E.A.R., GRAW, etc., however my current video card is a piece of crap. I was considering purchasing the XFX 6800 XT 256 mb ddr3 AGP video card for $146.99 at newegg.com. However, AGP is a dying (if not dead already) format, and I was wondering if I should just upgrade my entire motherboard in order to support PCI Express. I really do not want to spend more than $180 for a new video card and power supply, however I would like a few opinions as to what to do. Should i stick with a 6800 agp card, or should I upgrade to a PCI express motherboard and purchase a 6800 for that. I really only need 2 years out of this upgrade that I should be making soon, as I will most likely purchase a PS3 once the price drops. Whatever the case, I would just like a few opionions and a price range for what i could expect to pay for a new motherboard and video card.
Thanks

[goldeagle2005]

If you can, I'd suggest you get a new board and a PCI-E card. If you're on a budget, see that you get the best card you can afford. That oughta last you for 2 years.

[Bhstickman]

Well how much can I expect to pay for a PCI-E motherboard? Ive seen 6800 gt's on newegg.com for like $70, but how much will the motherboard set me back? I will also need to purchase a new power supply for around $30, because I only have a 250w right now.