It sounds like you still need ot removeIt from the Registry using Regedit.
Are you familiar with Regedit, It's pretty easy to use, But one mistake , and you can through your whole system out of wack.
i'll try and get the exact locations, etc, for you in awhile.
Also, Try restarting your machine. Sometimes that will clear everything also, and allow you to install. Also, Try installing from the CD Directory ie. D:/SFC/install.exe or whatever the actual path is.
Stephen