I haven't done it yet, as I've had other expenses get in the way, but my rig at the moment will consist of the following:

Athlon XP 2400+
ASUS A7N8X Deluxe mobo
2x 256MB PC2700
Antec True350 PSU
DIGN HTPC case
ATi Radeon 9500
Hauppauge PVR-250 cap card (Win XP MCE compatible)
Western Digital 2000JB HDD (will probably require a second one shortly)
Logitech wireless duo keyboard and mouse

I'll be using an external VGA to Component converter as ATi was kind enough to handicap their component video adapter.

Umm... I think that's it.

Thankfully, I have sources that can help me procure Windows XP Media Center Edition without buying someone else's over priced hardware.