Actually Vista 64 isn't as compatible with 32 bit apps as was first thought. I think I posted some links elsewhere regarding that. Basically there are some serious compatibility issues with it even with M$'s own products such as Office. The gist is that Vista 64 recursively updates the registry with keys and and values and ends up heavily bloated with millions of duplicate entries. Note that it isn't a complete incompatibility with all apps, but it is serious enough that some of the big voices in the IT world are staying away from V64 like it is the plague.