over a network if you have another pc, buy a cheap pack of cd rw's if you have a re writer, use an ipod if you have one, buy a cheap hdd to transfer onto . and thats all i can think of. i would personally buy some cheap rw's and do it that way or even dvd disks if your pc supports them
I have a PC in the corner here with 200GB hard drive, which we just bang everything onto when we need to, I also got a couple of encolsures and some 10GB HDD's somewhere, might fix them up later....
But yeah, I would say different computer if the best way, or a decent external HDD.
I use an external hdd most of the time. But if u don't have one and don't want to buy one then u could just ask if u could like take ur pc to a friend and put the files on his comp.
Also since we are talking about only 20GB if u have a dvd burner then u could just burn a few dvds. Using CDs would be my last resort since for 20GB u are going to need about 30 CDs.