The range of security features introduced in Vista and inherited by Win 7 provided an enormous boost to security. Unfortunately, those same security features also cause problems with some software that isn't designed for either of the two operating systems (OSs).

First things first, I recommend that everyone read the Tweakguide's Vista Annoyances article as this article already helps resolve many of the annoyances that many people have with these two OSs.

As for ways to get your software working, the first tip is to not install your software in either the "Program Files" or "Program Files (x86)" folders (latter only present in 64-bit OSs). The reason for this is because Vista and Win 7 utilises User Access Control (UAC) to apply special permission based protection to those two folders that basically doesn't give programs without administrative access permission to modify any of the files present. Hence, if you install or create mods, this can become a large headache. The reason this protection is present is because many important programs (eg. Anti-virus software) install their files in one of the Program Files folders by default (and this is the best place to install them). As a result, malware would require administrative access to modify your Windows or anti-malware programs' files, which (if UAC is set to it's default settings) only happens if you personally provide that access (ie. click the "Continue" button in the UAC prompt).

If, after installing your program outside the Program Files folder, your software still doesn't work, right-click on the shortcut or EXE for the program, click on Properties. Click on the compatibility tab then place a check in "Run in compatibility mode for:" then select the operating system you know it works for. Self explanatory.

If your program still doesn't work after this, right-click on the folder the program is in then click Properties. Click the security tab then click the edit buton. Click the add button then type everyone. Now select every line in the Group or Username box one by one and place a check in every allow checkbox except "Special Permissions". Click OK to exit every option window.

If all the above suggestions don't help you, go to the same compatibility tab mentioned above then put a check in "Run as Administrator" then click OK. Some programs that weren't written for Vista/Win 7 require administrative access to your PC to do what it needs to but also wasn't coded to request this access. Changing this compatibility setting forces your OS to provide adminstrative access when this program is run. Do be aware though that if malware infects this program, the malware will run with administrative access the next time the program runs.

Personally, I have only ever needed to implement the first suggestion to make Oblivion work under Windows 7 (ie. install outside the "Program Files" folder).