Fellow Total Warriors:
In ETW, a bunch of folders are created in C:\Documents and Settings\User_name\Application Data\The Creative Assembly\Empire\... AFTER the game executes.
These folders are also the location of your saved games in a save_games subfolder.
If you were using some sort of mod, be sure that you delete The Creative Assembly folder
and its subfolders BEFORE trying to reinstall Steam & ETW. If you want to keep your saved games, copy them somewhere else until you are up and running again, and be aware that these are most likley Mod specific.
Otherwise, when the game tries to start up, you will get the white screen with an error message "Empire.exe has encountered a problem ..."etc.
I hope this is helpful.
Gaius Flavius