JessZahn:I'm unsure, actually, about XP vs. Vista. Are you guys more on Vista or more on XP? (Not that that will drive the decision, but I'm curious.)
For us, Vista is more important.
We have two Vista systems and four MCE2005 systems (actually 5 MCE 2005 at the moment, but one needs a new home). I'll also be adding a new high end Vista 64 bit system (8+ GB RAM, another Quad processor, etc.) soon for a new project (it will run Media Center also, but no permanent tuner).
The main HTPC, doing the recording, is running Vista; but all of them are used to watch TV (~85% of the watching is actually done on the main HTPC).
STB w/R5000HD USB I/O, Gigabyte GA-P35-DS4, Quad Q6600, 4.0 GB RAM, ATI HD 3870 512MB, Ultra XVS 600W PSU, 3x SATA 500GB, 2x SATA 300GB, LG GGC-H20L, PVR-250, Toshiba 51H83 (51" HDTV), Yamaha RX-V2400 Amp, 5x Energy Speakers, SVS Sub, Harmony 880 Remote