The OS is only as good as the user, me personally I'm using XP on a number of machines and I can think of 1 instance where I've had to format a machine because of virus or spyware infection.
Ubuntu, Gentoo, Suse, they are all open same
I'm using Ubuntu Server as a server obviously and Suse as a desktop when windows isn't running. It's not all what's it's cracked up to me, sure if your the average joe blow using it for web browsing, school projects your going to be fine but if your like need and need certainly functionality which at this stage linux doesn't have your kind of stuck.
I will say though it is getting better and better all the time to back when I first dabbled with it back around the RedHat 6.2 days.
Anyways back on track, Vista isn't too badly priced, well in comparison to the pricing I've heard recently anyway.
Home Basic
Windows Vista CD 32bit $138.60
Windows Vista DVD 32bit $134.20
Windows Vista DVD 64bit $135.30
Home Premium
Windows Vista DVD 32bit $169.40
Windows Vista DVD 64bit $170.50
Business
Windows Vista CD 32bit $217.80
Windows Vista DVD 32bit $213.40
Windows Vista DVD 64bit $215.60
Ultimate
Windows Vista DVD 32bit $289.30
Windows Vista DVD 64bit $289.30
No I'm not going to buy it for anyone at that price
but it gives you an indication of how much you should be paying.