Windows ftp can fill up C: drive. This happens either putting or getting files, even if you try putting/getting them to a drive other than C:.
This happens because the ftp file is written to temporary area first by ftp, and moved to the final location at the very end.
The solution is to set temp directories to another drive which has a lot of free space, e.g.:
set TEMP=D:\junk set TMP=D:\junk
If running ftp from command prompt and getting large files, then just run those commands in the command window before starting ftp.
Otherwise set those as control panel environment variables.
A similar issue can happen with the oracle installer in windows, where it uses TEMP and TMP to unpack a significant amount of temporary installer files. Same fix in that case.