Other platforms and non-Mac network protocols that handle your file in transit don't know how to deal with forked files, so Mac files are likely to be corrupted when they arrive unless they have been encoded in a format such as BinHex4, which combines the two parts into a standard file. To un-BinHex, you need a functional Mac application that specializes in this sort of conversion. They are readily available, but unfortunately Macintosh doesn't ship a utility with their operating system, so you have to borrow from a friend or copy from an Apple friendly local network.
If you download a Mac application with only the resource fork in tact, it's possible to change it's type to APPL with a utility such as ResEdit, and provided it doesn't need the data fork it will then function. But this is somewhat dangerous, since it may try to access the data fork. I once used this method to make a functional copy of a BinHex decoder, which then enabled me to download decompression programs that had been BinHex encoded. In general its a chicken and egg thing. Best to go borrow one of the follwing: MacBinary, Unstuffit, Compact Pro, BinHex, Stuffit Lite, Stuffit Deluxe, etc.