Check the date on your dialog.tlk file. Has it been updated recently, or is it as old as (say) bgmain.exe?
A good way to check it is this:
- Check the size and date on dialog.tlk
- Install a new mod you've never installed before OR reinstall an existing mod but use a different language (obviously, it will need to be a translated mod--many NPCs, banter packs, etc. will do this.)
- Check the size and date on dialog.tlk again. If they are unchanged, it's a Vista problem, or you're just generically not installing mods correctly. Have you been through all of the basic support stuff on how to install mods properly (not running the game at the same time, not having editing tools open, etc.)?