I would like to replace the brake booster because I hear a small leak inside the cab every time I let off of the brake. Does this require me to drain the master cylinder? Or can I just remove it from the firewall and swap the booster and be careful not to bent the lines?

I've replaced boosters without removing
the brake lines from the master cyl. you
can unbolt the master cyl. from the booster
and remove the booster if you can get
the master to move out of the way.

Thanks - I was wondering if anyone has done this succesfully

Yes it can be done. You'll bend the brake lines to gain clearance to remove the booster, and then bend them back when you replace it. Make sure the cap is tight.

I've also done this. A set of shorty ratcheting box end wrenches will help with the nuts holding the boooster to the firewall.

I did this and broke a line. Big pain in the keester. If you can live with the problem, and it doesn't affect performance, I wouldn't dick with it.