running out of memory...not sure why

Sounds like you've confused memory and storage space.

At any rate, my bet is that you've got podcasts or some other form of regularly-added content taking up your disk space.

 

If you started creating iLife content recently, burning DVDs and such-like, it could be the encoded MPEG2 content made by iDVD during the burning process. Open each iDVD project one at a time and delete the encoded assets from the Advanced menu. Also see if you can't shift your iTunes or iPhoto libraries to an external drive, they usually make up the biggest percentage of drive space used on most system's I've seen.

 

Take a look at you hard drive's contents graphically using either/both of these free utilities- GrandPerspective or Disk Inventory X as they will make short work of being able to see what the largest files stored on your drive are to start with.