How to transfer files across two ssh connections

Hi, newbie question and I would be grateful if you could give me some

I connect from my home computer A to my work computer C by ssh'ing
into another machine B first, then ssh to machine C. However I can't
transfer files back from C to A, as B has a very small file quota
limit. How could I connect directly from A to C to transfer the files?
The login details are the same for B and C.

machine A: Win XP with putty and WinSCP
machine B and C: Linux Redhat