Is this card okay with this mother board?

Hi! I have a asrock p4v88 mother board with a pentium 4 2000mhz pt880 chipset and 1563 mb of ram. While I was looking at the AGP slot there's some writing about rails on it, and in the manual of the motherboard theres a warning on using a 3.3v agp on it. What does that mean? I was planning to get either an x1650pro or an x1650xt (agp) card, for my computer. Will that be an issue?

Second, I'm worried my computer isn't reallt that good, and that it might cause a bottleneck making those video card useless, is that an issue for me, considering these cards aren't high end cards anyway? Im just a casual gamer who enjoys playing old games at max resolution perhaps fable, or battle for mid earth, and maybe the occasional new games but would be happy so long as its playable.

Third, My computer is using a 300w PSU and i already have two 120 gig hard drive, a sound card, and two dvd burners. Im guessing there won't be enough juice to power those cards, what PSU wattage would you recommend?

Thanks guys

Thanks so I should start looking for a 400w PSU. But what about my motherboard issue? Should I just ignore that warning on 3.3v agp cards?