If you're going to buy a brand new PC, Windows 7 is the only option it will come with. Granted, there are stores that may still have some computers installed with Vista but you qualify for the free Windows 7 upgrade if you buy it now. All PC purchases after June 26th, qualify for the free upgrade.
You simply need to go to the manufacturer's website, submit your receipt info and they'll ship you a version of Windows 7 you can upgrade to. Depending if you're running 32 bit or 64 bit, the manufacturer will ship you the equivalent in Windows 7.
Also, I'd like to point out that Windows Vista did indeed have some flaws however after SP2 came out, those users that downloaded/installed this Service Pack have had no problems since.
So if you're going to buy an older machine with Windows Vista that does NOT qualify for the 7 upgrade, rest assured that once SP2 is installed, you won't have to worry about the excellent Apple attack campaign stating how much Vista sucks. ;-)
Shep