i have tried on both system and would lke to share my experience:
1) On Vista: unstable, MC 12 tend to crash Vista Home premium edition. Even re-installing MC12 does not seems to help. IT goes into reset mode even if you try to remove and reinstall again, it does not help. Some DVD rip files could not be read correctly.
2) On XP: More stable, but still faces crashing system if you have other codecs install inside your computers. Very sensitive to other hardware installed, so if you face problems of crashing, try to minimise having other hardware such as tv card or other htpc software.
I reinstall MC12 for more then 10times to find the bug for that 2 operating system. Definately, xp is more stable, you also need to be careful of other hardware or software that is inside your pc, mc12 are sensitve to them. Once incompatible, your system will go into rebooting.
I love this MC12, its COOL but certainly more work needs to be done to make it more stable.
my system:
Intel Duo 2 Core 2.4gz
2GB of Ram
ATI RAdeon HD2400 HDMI
2 Terabyte of Harddisk - Sata II
Auzutech Xplosion 7.1ch DTS sound card
Silverstone HTPC case with Imedia, IMOn