Hey,
Just install the game again, EXACTLY the same as you did before (same game folder, same components installed to your hard drive, etc.).
Then go to the "configuration" part of windows (I guess you have XP) and go to "software". Click on the remove - button (the upper one of several large buttons), and search in the appearing list for that game. Select it, and click on "remove" (at the right of the name of the game). Now will windows remove the game from the register, though some components might not be removed. If lastmentioned is true, then just remove those items (e.g. the game folder) manually.
I hope I have helped you with this

!
Richard_Rahl