Time machine able to use an already-used drive?

[AGSHender]

I have an external firewire drive that I use as an archive drive. I just bought a new MacBook Pro this week and would like to use it as a Time Machine backup destination, but since it's already being used to store other files can it be used by Time Machine? Or does Time Machine have to use a blank drive? Any help is appreciated. Thanks!

 

[emt1]

Just add it in Time Machine settings. It will be fine. It's a Mac.