you ran regedit and ctrl_F "BATTLEFIELD VIETNAM" (without quotes) ? delete anything there, also make sure you turn off anti-virus when before installing, if you have an anti-virus program that is.
EDIT: ok ok, i found something, try this:
"Do the following in order to uninstall:
1. Delete the folder (including all sub folders), from where the program was installed. Default is C:\Program Files\EA Games\Battlefield Vietnam
2. Go to "Start", then "Run", then type there "regedit" and hit ok.
3. At the top left side, select "File", then select second choice "EXPORT", you will need to enter a file name (like: RegCopy07142004), and select a folder or c:\ to place your "backup" exported registry. (In case you need to, in case you make a mistake... you can return to the registry and use "Import" to get it back.
4. Under "Edit" hit "find" (Ctrl+F)and type "Battlefield"
5. The 2 folders that will find and you need to delete are: (do not delete any BF1942 if you have it):
HKEY_CURRENT_USER\Software\Battlefield Vietnam
HKEY_CURRENT_USER\Software\Microsoft\Windows\ CurrentVersion\Explorer\MenuOrder\Start Menu2\Programs\EA GAMES\Battlefield Vietnam
If you search for more "battlefield" it might find some other minor keys you might want to delete or not (not critical to the install).
Try running Disk Defrag as well, then try installing the game again.
Let us know how it worked out."