Sorry, I don't know anything about Vista ... but this might be of some help:
http://mysql.blic.net/doc/refman/5.0...tallation.html

According to the manual 64-bit windows vista is not supported.

I found it via a search in google. The query I used was:
troubleshooting mysql installation windows vista

You can try the same query yourself, as there may be some other helpful resources in the same SERP.

Hope this helps.