I have an Antec Trupower 480W that I got about 3-6 months ago (can't remember exactly). I am currently running:

abit av8
2gb pc3500 kingston
athlon 64 3500+ (2.2ghz)
RAID 0 array - 2xWD Raptor 10k rpm
1x80 GB Maxtor 7200
plextor dvdrw/cdrw
audigy 2
sapphire radeon 9800 pro

Edit: Also running 5 80 mm case fans (low speed), and one high speed 80mm Delta on my processor.

And I'm planning to upgrade the mobo to something with an nForce4 SLi chipset and probably a 7900 GT (not in SLi config, just 1 card for now). Am I likely to have any trouble pulling that kind of power draw or do you all think an Antec Tru480 can handle it?

I would say you are close to your limit, there is a program I think that could show you the wattage used by each item here are some #'s I saw in a review of a power supply
3000+ Clocked to 2.52GHz (280*9, 1.61V, Drawing 124W)
DFI SLI-D With all power connections made (20W)
2x NVIDIA 6800GTs (Drawing 100W each)
2x512MB OCZ GX Memory (Clocked to 252MHz @ 2-2-2-0, 3.33V, Drawing 80W)
Leadtek TV2000XP Deluxe (Drawing Mere Standby Power)
2x80GB Maxtor SATA Drives, 1x250GB WD PATA Drive (60W Draw on 12V/5V)
LG Combo DVD Drive (20W Draw)
Assorted cooling care of a shed worth of fans, 10W
Total Wattage Needs Estimate: 574W!