Need advice on a PSU for new card

[cluedo84]

Heya!

I recently purchased a new Leadtek Winfast GF 7950GT 256MB fom my computer, but have come to realise that my current PSU is woefully inadequate!
I have read that the 7950GT is comfortable with a PSU with at least >20A on the 12V rail.
I am planning to get a( http://www.acbel.com/PDF/P_PC/ps2_550W_gold.pdf ) which has 3 12V rails at 12A, 22A, and 14A respectively.

I know that they don't stack up exactly but i'm kinda confused of how that multiple 12V rail system works. Are there three 12V cables that correspond to the 12V rails? Or is there only one 12V cable fed by the three 12V rails? If there is more than one cable, what do i use the other 2 cables for and do i stick the 22A cable into the motherboard? (heh... sorry, i'm really a noob at computers!)

My current rig is
P4 3.2GHz, 1 GB RAM, 2x 100GB HD.

Lastly will this PSU which i'm planning to get be able to support the new system?

Thanks for your time and i hope to hear from you guys soon!

[EDIT] More details about my rig (from the invoice)
Processor - P4 / 3.2GHz / 1MB/800
Mainboard - GIGABYTE 945P/DDR2?GL/PCIE/ATX
Memory - Kingston 512mb/533/800/dr (i think i have 1 GB ram in total)
Harddrive - Seagate 40GB /2.5"/ATA100/5.4K (i think 2 units)
(Not sure what half this stuff means! =P )

[jonnyGURU]

That's a good PSU.

I think the way the +12V rails go with that thing is one to the CPU, one to the PCI-e connectors and one to all of the Molexes.

It's enough for you. :D

[cluedo84]

Hmmm... but how do i know which cable i attach to the different components? like where does the 22A, 14A and 12A go?

[jonnyGURU]

It doesn't work that way.

The rails go to a certain connector type. It's not like one rail goes to some Molex connectors while other rails go to other Molex conectors.

There's one rail that provides power only to the 4-pin and 8-pin power connectors. Then another rail that provides power to just the 6-pin PCI-e power connectors.

[cluedo84]

ahhh... so its kinda idiot proof? haha! Thats what i really need! Sorry for the noobish questions!
Anyway i'll try to examine the PSU as soon as i get it and READ THE MANUAL CAREFULLY to see how the connections work! i cant plug it into my PC till next year anyway =P

Thanks a million man! You've been a great help! Hopefully i dun screw it up too badly! will be back if i have any more problems!

Thanks again!