I am wondering how the ampere rating work for a PSU. I have an Enermax Liberty 500w, and it states that I have 22amps to each 12v rail. I've read that I'm supposed to 26 amps to my 8800GTS in order for it to run, but it seems that its running fine. I havent had any random shutdowns or anything like that since I installed it, even after 6-7 hour long periods of gameplay in CoD4.

But I also read somewhere that when only one device is plugged in, that the amps from each rail combine? I didnt think that was true, so I thought I'd ask here.

I am no expert on internal Power Supply functions-- but these guys would be:

Question about recommended amperage on PSU 12v rail for Video Cards. - Sharky Forums

Basically their recommendation was that-- if you have a good quality PSU-- like yours-- and you have the motherboard and Graphics card on different rails-- then you should be OK.... which is what you've been getting.
The risk with weak PSU's-- is damage to the video-card, apparently.

This is why I am always pushing people to buy good quality PSU's from reputable companies...
the power-supply is the most under-rated part of any PC
they are not glamorous or sexy-- but if you don't have a good one-- nothing else you buy will work to it's full potential-- and you can even damage those fancy parts

im not positive, but the 2 12V rails combines come out to 44 AMPS, plus they always exgaterate those numbers. I was running a Geforce 6600GT on a 305 watt power supply before (reccomended 350) with absolutely no problems. those numbers are way overstated. Im running the same PSU you are with a C2D @ 3Ghz, a Geforce 8600GT Overclocked, 2GB RAM, a SATA HDD, and soon a WD Raptor too. have no fear. the Liberty is a tough little bugger

The numbers they recommend are definitely conservative... and a good Power Supply Unit will survive-- If you were running all that on a cheapo ($30.00 US) Power supply... you would have seen smoke by now... and the trouble is, when THAT happens it's likely to take motherboard/RAM/and Video-card out with it. The Cheapos are what you usually get with a case-- not always, but most times.
$800-$1000 dollars in one puff of smoke-- is too expensive for my taste.

I just recommend going higher on PSU ratings-- and buying from a good maker... this is because there is no government testing/regulation agency for PSU's-- there is no UnderWriter's Labs for computer parts-- therefore it's "buyer beware" -- which means there is a lot of cheap junk and a very few reliable brands.
My point is-- if you are going to spend that hard-earned money on all that fancy gaming hardware-- literally thousands of dollars-- it is foolish NOT to overkill on the PSU-- you not only get maximum performance and life out of the gaming stuff-- but you leave a little "headroom" for possible future upgrades.
I generally use a PSU calculator-- add in whatever I think I might want in the future-- and add 75-100 watts to that number-- and that's what I buy... if I have to compromise-- I go higher, not lower.