This used to work nice and dandy for Leopard 10.5, but with Snow Leopard (10.6) it picks the wrong printer driver and uses the CUPS one. This is because for some reason the HL-5070N BR-Script3 driver is NOT supplied on the Snow Leopard DVD. grrh
I was banging my head for a long time (I hate printers and wanted nothing to do with it) and googling found no results. So in order to help any wandering lost souls, I thought I would write it up.
As I mentioned, when you set up your printer (SystemPreferences -> Print&Fax) and then add printer, it says it's using "Brother HL-5070N series CUPS". This is WRONG. Well its wrong for me anyway.
If you try printing you will get something like:
ERROR NAME; undefined COMMAND -12345X@PJL OPERAND STACK;
Useful isn't it? :)
So you need to pull the OLD printer driver from Leopard (10.5), to get this puppy to print.
It's called 'Brother HL-5070N series.gz' and is under: /Library/Printers/PPDs/Contents/Resources/Brother HL-5070N series.gz
If you look at this directory in Snow Leopard, the driver isn't there.
So drop that file Brother HL-5070N series.gz into the same directory in Snow Leopard (don't uncompress it), delete and re-add the printer and it should say:
Print Using: Brother HL-5070N BR-Script3. This is RIGHT!
Let me know if this works for you.