Oh go away you n00b!

Just joking. OK, so I looked into the 9400GT. Apparently there's sporadic drivers being tossed around for it so it might indeed work. But if I were you I'd Google around for a more likely to work card before putting down $$$ on a card for the sake of good Hackintoshing.
As for the mobo...bleh, the old one's an nForce. No wonder you've got issues. The board you're looking at would definitely be a better choice, though you should probably be able to find an SB600/700 mobo for a bit cheaper than that one unless you really need 3 PCI-e slots.
As for what a distro is...notice how there's differently named prepatched OS X discs floating around (eg. iAtkos, Kalyway, iPC)? They're called distributions, or distros. Simple as that.

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Custom Hackintosh...AMD Athlon X2 5000+ (2.6 GHz) on GA-MA78GM-S2H...Linksys WMP300n Wireless...ALC889a sound...ATI HD 3650 PCIe...1 GB DDR2 RAM...320GB Western Digital SATA + 200GB Seagate IDE HDD...Rosewill DVD-RW IDE...Running Kalyway upgraded to 10.5.7...All Fully Functional