How can I move messages from my inbox to my computer, completely out of outlook.

My office only offers 100mb of email storage and I'm almost there...my graphic files are HUGE.  

I have tried to MOVE to "my computer inbox" but that doesn't seem to take it out of the limited storage area.

I MUST keep the copies of the incoming and outgoing messages and be able to easily access them, but I need to have them somewhere where they won't effect the limited storage capabilities.

I am one of very few in our company that uses a Mac and my email is connected to the company server (PC).

Thanks for the help.