Install on multiple PC's

Hi Guys

I need to install Microsoft communicator 2005 on 50 PC's, any ideas on how I can do this? do we need to download any special software?

This is how it is

- all PC's are connected on a network/domain
- all PC's are running xp pro
- all users login with their userid and pass. And their details are in Active directory

How can I install it all it once when they login to their comps?

Thanks