Most external drives get formatted in fat32 by default.. and nowadays Mac OS can read and write to that drive...
However if it has been formated to hfs or hfs+ your not going to be able to read it directly into Windows, obviously.
Linux has limited support for HFS/HFS+ file systems and good support for fat32. So if you have a fat32 partition on your harddrive you could possibly boot up with a knoppix cdrom and copy the information over that way. Although I don't know if knoppix supports hfs partitions out of the box.
Otherwise the best bet is to get your old mac and transfer the stuff over the network using a file share from your Windows box.
Those are the options that I can think of now..