Power supply question

I'm concerned with the current power situation of my gaming rig:

XP 64 bit

AMD Athlon 64 X2 4600+ Windsor 2.4GHz Socket AM2
XCLIO GOODPOWER 500W
2x G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800
ASUS M3A79-T Deluxe AM2+/AM2 AMD 790FX ATX AMD Motherboard
BFG Tech BFGE88512GTSE GeForce 8800GTS (G92) 512MB

1 HDD and 1 DVD-RW

(I hope that's all the information needed, if not I will post whatever else is needed)

My concern is the power supply. I know the 8800 gts is power-hungry (wants +12v1@28amp) and my power supply is only rated for +12V1@16A. It runs fine while doing moderate gaming (Far Cry 2 - all on medium/high some ultra high) but my when it comes to my main addiction - WoW, it has some problems.

The machine will run just fine in normal-medium conditions, but once i get into a 10-man + raid, it bogs down to a crawl (seems like 2-4 fps).

Could my power supply be causing this? I know it doesn't pump out the right amount of amps but before I go out and purchase a new psu (looking at this one currently: PC Power & Cooling S75QB 750W ATX12V / EPS12V) I'd like to get an expert opinion.

I've tried everything from many different vid drivers, setting all video settings to their minimum and removing all the little extras I have, yet the machine still preforms horribly when faced with the raid environment.

Thank you for your time in responding to this. I've poured over the web for the past few days, trying to find a solution (I'll admit, I'm not savvy with the psu output terminology, I've read up on it yet cannot fully grasp the content's meaning) so with tail between my legs, I've turned to the only source for trusted answers.

Thank you and game on.

EDIT: I'd like to also mention that I may be adding a second 8800 gts in the near future as their prices have dropped dramatically with the release of the 2** series from nvidia. I cannot fathom the whole dual-rail balancing act so I also beg of thee to perhaps suggest a psu in which could accommodate two of these gpu's?

Again, thank you very much for your time.

you need 750w good psu for sli

silverstone 750 antec 650 tiple antec 850 on sale alot

Wow! Such fast responses, thank you!

I too, am looking at my 4g of ram with some questions, most certainly will be upgraded to 8gig come Christmas specials.

As for the psu suggestions, I've looked at all and noticed that the highest amp output on the 12v was 22 amps. Would that provide enough power for this sucker (since Nvidia recomends at least 28amp)?