You can load all the files into the temporary internet files folder on probably most school computers that run stuff like fortress101 and all that junk.
And as for 56k, honestly wtf? C'mon, yeah its quake2, but its also 2006, tell your parents that you're getting owned by the lag. If you're stuck with 56k and a cheap mofo then yeah, you do need to go to a friend's house to burn a CD, just be glad you aren't a quake 3 or quake 4 addict too.
Also, if your neighbors have WiFi, make yourself a cantenna.