My startup disk is full...can't access anything

My startup disk is full, and can't even get in to anything to delete stuff, how can I get in and move things to my external hard drive (which is what I was doing when it somehow became full)? All that happens is I reset the computer, when I turn it on it says the start up disk is full, I put in my password and the screen just stays grey. I also noticed before I started moving things that the "other" storage of my 60GB macbook air was over 30GB, but not sure how that could be/what it is. Mainly just concerned with getting the photos and things from my computer to my portable hard drive so if anyone can help that would be great.

Cheers,

Sam