I just moved from a Windows XP computer to a newly built Windows 7, for Skyrim and other games. But I'm still playing Oblivion too.

In XP I would create different user accounts for different types of characters. That kept the saves separate, but more significantly it allowed me to activate different mods per type of character (eg a Noble Warrior would get different mods than an Evil Necromancer).

I reloaded Oblivion, DLCs/Expansion, and all mods from scratch, thinking that would be safer than simply copying the full Data directory.

I was able to get a character save from the XP system to run in the main (admin) account of the Windows 7 system. Then I created a second account and appear to have problems. Specifically the save I moved over is from Frostcrag, and the walls/floor are untextured and solid purple. The are likely other problems. I made the second account an admin account with the same problem. I also made sure that the User Accounts had Full Access to the Oblivion directory (under C:\Games\Oblivion, not under Programs).

Any thoughts on what might be causing the problem or how to fix it?

Thanks!

The DLC doesn't unpack correctly with 64 bit W7. Try just copying over the Frostcrag and other DLC content to your new Oblivion installation.