I use mldonkey under Linux. When you start download something, it reserves all the necessary space for that file. But the space it's not actually used. If you do:

df -h

you see what I mean. But I tried copying the temp files to a SFS partition, so I could share the download process with the MorphOS client. But then, those files occupied the real space ^^;

The best thing is using ext2 (ext3) filesystem? whadja think?

feel free to port ext to mos
otherwise you won't be able to use those partitions under mos