I can sympathize with the poor side of it. Been there, done that. Nothing wrong with the barebones you've picked out, but I'll give you a word of warning (or two).
One, I hope you don't expect to actually get the rebate offered by Tiger Direct. Too many people on these forums have been screwed by them (well, by the company that does their rebates, anyway). If you can't afford it without the rebate, then don't get it.
Two, make sure that your RAM will transfer over. I figure that you're going to strip your old system to make the new one (it's what I would do). Since your current system is a P3, it's RAM may not be a current type. Plus, it is probably really slow RAM to boot.
Three, you will have to reinstall XP when you fire the new computer up. XP takes a snapshot of your system specs when you install it, and updates it when things change. If you take your hard drive and slap it into the other rig, XP will not boot, as it will see that it is not the computer it was installed in.
Not trying to dissuade you, but inform you.
My Rig: SABLE
Antec 300 Illusion / Antec EarthWatts EA650 650W / EVGA GTX 760 2GB
AMD FX 8320 x8 Black Edition / Gelid Tranquillo / MSI 970A-G43
Sandisk Ultra Plus 128GB / Samsung 840 120GB / WD Black 750GB / WD Green 1TB / WD Red 3TB
G.SKILL Ripjaws 2x2GB DDR3 1600 - Crucial Ballistix Tracer 2x2GB DDR3 1600
Win7 Ult 64-bit - Func MS3 Mouse - CM Storm QuickFire Rapid Mech Keyboard
R.I.P. Danny L. Trotter
... 14 Nov 1945 - 4 Sept 2009