OK. So to summarise the current Mac situation:

1. Firefox doesn't download numbered files correctly. Use Safari or Chrome or something else.
2. MacHacha works great to join the numbered parts together. But it won't split them.
3. There still is no simple way to split files into numbered parts. The split command in terminal generates files called xaa, xab and so on. That's fine for macusers because you can use the cat command to join them. But that's no good for everyone else. Else you need to rename them.

Any suggestions for simple software that will do what hjsplit does on OSX would be appreciated. I've got a bunch of files I could split and upload but can't…*Any coders?