I've used DFI and ASUS boards up until my p35 asus died last year.
Gigabyte now a days has a much better rep.
seagate 1tb

- again another used forever situation with seagate, but swap that 1tb .12 series for a
western digital BLACK 1tb (not blue or green) it should be nearly the same price or less. 2 reasons the black is nearly as fast as the velociraptor (fastest consumer mechanical drive) and faster than that 12 series barracuda, plus a few years ago seagate switched to 3 year warranties and wd is now 5 years not to mention lately seagate firmware has been flaky
sapphire cards

- one more suggestion avoid sapphire, get
xfx if you can. XFX recently switched over to ATI from nvidia and well their warranty and support is 10x better than sapphire or any ati partner.
750w truepower

- normally I'd recommend the PC Power&Cooling silencer 750w over anything antec has been making lately, but that 750w truepower is way better than antecs usual stuff its a solid psu.
edit: can't believe you still game on a athlon xp! system, i've gone through atleast 6 builds since my good old 2500+, anything will be a giant leap from that system.
back to my point: any particular res you game at? anything less than 1650x1080 and you're really dependent on cpu power for mostly anything.