I run dual boot with Win7 and Ubuntu. Ubuntu, on my dual core/ 4gig laptop is far faster than Win7, it boot's up in 12 seconds, you don't require antivirus, spyware, malware etc. It's free, it has all the software you could want using simple add or remove. It also runs all my windows stuff. But it is a learning curve, if you do more than surf the web and the odd office doc it can get abit confusing if your used to windows, but there is plenty of support. I recommend that you, as suggested above run the Ubuntu OS from a live cd, basically you do not need to install it. you can also from the live cd access all your microsoft HDD! I have used this to repair currupt windows before. Also to buy a laptop without windows it is cheaper.
In this case if I was you though I would install/ dual boot seven and your current Vista. To do this do a clean install of seven onto a new partition. Once you have it up and running you can experiment with Ubuntu.