I have a keyspan usb to serial connector ((2 serial ports) connected to a prehistoric opcode serial interface) and although the manual swears black and blue that it won't pass midi data - it does!
Works on Metro 4.5 and Metro 5 under 9.1
See no reason why it wouldn't work under 9.2 at least.
Will try it one day on 10.2
NOTE: for the price of the keyspan though, you would probably be better off just buying the usb midi interface. I'm sure you can get a cheap one.....probably less than the keyspan.
Are you wanting to stay serial for other reasons? (printers?)
If not go USB - I will too! - one day but would rather fork out for it built into a tascam US-428 than just buy a seperate device I won't need later on.
Good luck with your decision.
scoot.