I’ve heard a number of tech experts including the esteemed Mr. Lloyd Case from Extreme Tech podcast as well as others like Steve from the Podnutz podcast state that there is no way to do “repair install” in Windows Vista similar to XP, or all recent editions of Windows for that matter. Actually Microsoft has given Vista users a way to repair Vista with the install DVD, they're just hiding it a little. And although Vista doesn’t make it obvious like it used to be, it still exists.
So here’s where they're hiding it, you get a repair install in Vista by doing a “In-Place Upgrade”.
1. Start the computer boot to Vista OS.
2. Insert the Windows Vista DVD in the computer's DVD drive.
3. Use one of the following procedures, as appropriate:
If Windows automatically detects the DVD, the Install now screen appears. Click Install now.
If Windows does not automatically detect the DVD, follow these steps:
a. Click the Start Button, type Drive:\setup.exe in the start search box and then click OK.
Note: Drive is the drive letter of the computer's DVD drive.
b. Click Install now.
4. When you reach the "Which type of installation do you want?" screen, click Upgrade to upgrade the current operating system to Windows Vista. Please make sure the edition of Windows Vista is selected correctly.
I didn’t get these instructions by reading a 1000 page manual, I got them from Microsoft when I needed tech support installing SP1. I followed the instructions and it worked great for me. Of coarse if you’re doing anything this extreme make sure you have a full backup and are using the correct disk. If you have SP1 already installed you need have a SP1 disk to do what Microsoft calls an In-Place upgrade (Repair install) in Vista.