Help a PC switcher with install

I've decided I'm going to do a clean install on my new Intel Mac just because I'm OCD about my computer running perfectly. I need to basically reformat my PC's external hard drive so I can use it to back up my Mac. Will I lose iLife by doing this? And will my old programs, like MS Office, reinstall in Leopard with the old Tiger disks? Thanks in advance.

 

My main question was really how do I get my PC's external harddrive to be formatted for my Mac.

Will I lose ALL software, such as GarageBand? My iLife came preinstalled so I'm not sure I have disks for it. Do yall think a clean install is really necessary? I haven't really had many problems up til now with Tiger.

 

Dan! That's exactly what I need to know. Can you direct me to some directions on how to accomplish this?