I have sat on my desk, and sew setup, MSI 785GM-E51, Athlon II 245, 2GB DDR-3 1333, and a Samsung F1 320GB HDD, running XP SP3, and I have just benchmarked it using the classic old PC Mark 2002, and 3D Mark 2001.
I got on PC Mark 2002 - CPU 10,124 - Memory 20,150 - HDD 2372. 3D Mark 2001 gave me a score of 13,972, and that is with only 64MB of RAM given to the onboard graphics (this board does not have sideport memory.
Its pretty cheap overall, here are the main components.
(2 of these, well not exactly, but its an example)
The reality is that this system with its integrated graphics is not far off of the performance of your 9600xt, and the rest of the system will make your old system look pathetic. Overall the system will likely end up using about the same amount of power under load, and probably somewhat less at idle. You might need to get a new HDD/ODD at the same time as modern motherboards only have one PATA channel. The fan that comes with the CPU is actually not that bad (compared to OEM fans of the past), and the chipset simply does not need any fans.