Yep, that card will work fine on your mobo, the 2.0 is backwards compatible. I'm an nVidia fanboy, but as i have told many other people, the new AMD video cards(the 4xxx series), are supposed to trump the 9800gtx in performance. The 4850 is only supposed to be around $190, and better benchmarks than the 9800gtx. Charts:
So, I would wait until the 25th of this month to get a new video card. As for your PSU, I would get that one, as it is just fine. I would suggest getting that right now, and then buying the 4850 later this month. IMO, this is what I think you should do. Your 7800 should last you a few more weeks, right?
btw, all of this is if you're not planning on SLI. If you are, I'd still wait until the prices drop, because of the new gtx 200 series.