Most recovery files from an OEM are stored on a recovery drive. This drive sometimes doesn't get a drive letter. You can only see these partitions by right-clicking computer from the start menu and using the disk utility. Installing windows 7 will not overwrite these recovery partitions. However, specific software is sometimes required to give you access to this recovery drive and usually, that software is only on the original install by the OEM.
You should backup your vista using DVDs. This options should have been provided to you by your OEM.
Usually, there is a hotkey that OEM give you that allows you to access the recovery drive. It is independent of software and connected to the bios. For example, on my laptop, by pressing the F8 key right after the bios screen, I can access my recovery partition.
If you install windows 7 on a separate partition, Windows 7 cannot overwrite your vista unless you choose to overwrite vista (this is on a custom installation). You will get a dual boot situation where you can choose to go to either vista or windows 7. Be careful when making a partition for windows 7 that you don't erase the vista or recovery partition.
