Leopard Users: Time Machine Questions

Sorry if this has been addressed before, I tried searching the forums for similar questions but to no avail. Apple docs have also been unhelpful.

I'm currently running 10.4 on a 12" Powerbook. I just bought 10.5 and I'm planning on installing it this evening. I have an external HD, half of which I use to store my movies, and the other half I use to back up my Home folder. I'm planning on using it with Time Machine, but I have two important questions:

1.) Does a Time Machine drive have to be dedicated? - In other words, will I have to use my entire external HD for exclusive use by Time Machine? Ideally I'd like to be able to configure it so it only uses half of my drive, and leaves the other half (my movies) alone.

2.) Can I specify how much Space Time Machine uses? - This is closely tied to the first question, but more generally, can you define how much space Time Machine uses for backup? Or does it keep adding to your drive till full, no questions asked?

These points could be deal breakers for me. Thanks for your help.

 

So Time Machine will fill the free space in my drive until full. You think they'd have made it more customizable. Will it not touch my movie files? Or will it write over them in a bid for more space?

 

That's the answer I was looking for. Thanks for your help.