I've only tried out "Melty Blood: Re-Act" on vista and i know that works, i've never tried out the "Melty Blood: Act Cadenza ver.B Demo" on vista yet so i don't know about the problems your having however you seem to be a bit confused about something. There is no version of "Melty Blood: Act Cadenza" for the PC, that game is a re-balanced arcade port only released the PS2 on august 8th 2006, The Demo you have for the PC is for "Melty Blood: Act Cadenza ver.B" This however has been confirmed that in June, Melty Blood: Act Cadenza ver.B will be released for PC as well as the PS2. So if that is what you've been trying to find that online to buy, you'll have to wait another 2 months or so, the exact day i dont' know but thats the month its planned to release. Hope that clears up why you can't seem to find the PC version.