Minimum Hardware To Run Windows 7 'usably?'

So, I recently installed Windows 7 on my aunt's old PC: Pentium 4 Prescott "A" 2.8GHz, 768 MB RAM, GeForce FX5200. Runs quite well, even with glass on and MSE running in the background.Now, my mom needs her computer reformatted. It's currently running Windows XP, and I wonder if it can make the jump to 7: Celeron 1.2 GHz (I do believe it's a Tualatin, though; if it is, that makes it as good or better than Pentium 4 Willamettes) 512 MB PC133 SDRAM, and some newer nVidia PCI card.Can it manage it? I actually made Windows 7 "usable" on a Duron Mobile 800 MHz with 512 MB RAM and integrated GPU before.