(not sure about all but generally) all the distro's will install as dual boot by default if you have another os installed already, i have done this with windows 7 and ubuntu (among many many other versions of either windows or linux) but it is ALWAYS a excelent idea to have another backup just incase
..... you really never know if it's going to go as smoothly as it should.
oh, and for some reason.... if you decide to scrap linux later (or remove the HDD), the windows 7 repair tool for some reason doesn't detect that the computer is trying to boot to grub (linux boot loader) rather than the windows boot loader, and will not fix it (thus you'll have to reinstall everything, yada yada...) what I did.... is before removing linux, i used the backup tool in windows 7 (now does a real backup complete with system image and all) to back up the windows hdd then after reinstalling windows i ran the restore utility, all settings, drivers, absolutely everything was back to normal and peachy keen. (the restore did take a few hours though)
good luck in linux!! i LOVE linux, but it can be annoying here and there if you're not used to it (such as using WoW and Ventrilo, etc...)