On second thought, what a bad idea it is to build a desktop PC, and it's not XP's fault btw. So far I have an Ivy Bridge CPU + mobo + 8GB RAM. Originally, I had planned to make this desktop a media PC, mostly to play games b/c you can insert a graphics card into the mobo, whereas in a laptop, I'm stuck with the Intel integrated graphics.
Anyways, I tried out a few 3D games/movies on our current desktop with a 26" LCD monitor, which had mostly been used for word processing/internet browsing/other productivity-related tasks. I can sum up my recent experience in three words: nausea + bad graphics.
Apparently, 3D games were designed for a 15" monitor or smaller. Any larger and it's instant nausea roaming around the virtual world.
As for playing movies. I test screened a few MKV vids sized approx 4GB. If MKVs are to vids what MP3s are to music, then a 4GB MKV video would be the equivalent of the best MP3 encoding at 320kbps. Apparently, even such a high quality encoding will appear blocky on a 26" monitor up close. Not only that, I found that it was difficult to adjust the tilt angle of the monitor for optimal viewing so that the dark part of the screen doesn't have any light from the backlight spilling out over it. In reality, I obtained a higher quality viewing experience on my 14" laptop than the desktop with 26" monitor. No wonder why consumers are so keen into 4K monitors now, b/c 1080p just plain sucks on desktops, but not so much on TVs where they are further away from you and it's more difficult to make out the pixelations. And if there's one thing XP doesn't really support, it's 4K monitors...
Anyways, I'll probably end up using the parts I have collected as spares for our current XP-capable desktop, or sell them. As it stands, it sure looks like I'll look keep my mobile XP systems to last for another decade or two, as they offer the best experience in both gaming and viewing high-bitrate encoded videos and in productivity...