key code to our application

Question

hi,I am currently working on winforms application once I finish this ie when its get ready to implement in pcs , i would like to add KEY code to it(for eg u might have seen while installing xp cd, it ll ask for 25 digit key code )... in the same way whenever some body wants to install my project they should give that keycode at the time of installation.... pls suggest any ideas to accomplish this.