Ok, I'll bite...
I would categorize your assessments of Vista, Joomla 1.5 and JFusion as "inaccurate" at best.
Joomla 1.5 has no bugs that I've seen and almost every extension that works in 1.0 also works in 1.5 with legacy turned on. Migration is a snap if you handle the extensions separately. Legacy extension database tables can be manually imported without any migration at all, so you just migrate the core, install the extensions and then drop and re-import their database tables from your 1.0 install. Bing, bang, boom, and you're done.
As for JFusion being "laggy", it sounds like you need a better hosting service. I actually only use JFusion to frame the forum into a Joomla component page. I use the RokBridge Joomla to phpBB (the best board on the web) bridge. It's the bomb.
Regardless, it sounds like you have a completely different issue than I did. Sadly, it's an issue that would be eliminated if you upgraded to modern software.
As for Vista, it's the most sophisticated and powerful operating system ever created and has no more problems than any other. That is a myth perpetuated by people who have more money than brains (aka Apple owners) and others who have some unrelated problem and blame it on the OS. Bad-mouthing Windows and/or insisting that XP is better than Vista shows extreme lack of experience with computers and computer users.
For the record, I am no cheerleader for MSFT, I just recognize that they happen to have the best dog in the race for the average user. From a technical point of view, Linux is my new fave. I am however, a happy fan of Joomla.
Keep it light, fellas.