Welcome Xiren!!
Now *could* be a good time to switch, but it could also be a good time to just stand pat for a while.
The release of Vista doesn't mean that you have to go out and get it right away. In fact, you would be well advised to stay away from it for 6 months or so, while the inevitable batch of major initial bug fixes goes by. Let someone else bear the pain of that. If you really want Vista, pick it up in six months or so.
Meanwhile, if your Windows box is serving you well and you are happy, no need to switch.
Now if, on the other hand, consideration of Vista inspired upgrades has ignited a desire to upgrade anyway, this is a great time to switch. Again though, I would recommend standing pat for a bit. Apple is about to release Leopard, the next version of Mac OS X. Macs are good, but they aren't perfect either. I would wait for Leopard to go through its initial round of bug fixes before jumping in.
So, in general, my advice would be to stay on the sidelines for a while longer. From your post, it doesn't seem like you are really eager to get a Mac, rather you seem to be weighing the cost of upgrading your PC to support Vista vs. the cost of a Mac. If Vista is the driver, wait it out a bit and then compare everything you are hearing about Vista vs. Leopard.
In the end, I am confident that you will find Leopard to be the more compelling of the two.
Now with all that said and done, if you are in throes of techno lust (been there myself, done that, got the T-Shirt, more than once!) and are going to buy something, soon, no matter what, right now is GREAT time to upgrade to a Mac. If your choices are PC or Mac, there is no doubt. Go Mac.