External hard drives are very cheap. I suggest purchasing one or reevaluate your storage space. I'd be in the same boat if I didn't have mine or my back-up. Other advice, if you can't get one quite yet, you can probably delete any old podcast episodes since you can redownload them when you want to take a listen and whatnot.
I have a terabyte external drive that I can move some stuff on to, but out of the 93 gigs I use, 89 of its iTunes. Deleting podcasts though would only be 1 gig, as I have only my favorite episodes on my comp right now.