Mainframe Gurus or Dosemu Gurus :)

I know I said an evil word in relation to this list ;), but I need a
spot of help.

I'm taking the COD Assembler class (need to to get the COD Advanced C++
class), and it's all in S/370 assembler.  Now, we aren't using a real
mainframe, we are using some wierd software called PC/370 for dos.  I
have a slight problem... I have had no dos/windows systems open for
development for years, and I'm not about to go and reboot just to
assemble and test.  Now, I have tried setting up a basic privleged (I
think) Dosemu session and tried to run the assembler/simulator and it
just gives me the error "INTERRUPT IN USE".  I'm not sure if it's
freedos or dosemu killing it.  Now, my second option would be to setup
hercules and run a full MVS session.  My problem with that is, being
from a PC/Unix background, this is very confusing and I can't seem to
get a list of files (or datasets or whatever) on the system through TSO,
and if I'm going to use MVS itself for it, I need to learn a bit of JCL
to get that to work.

Anyone have any thoughts, or can anyone give me a hand with this?  All
help will be gladly appreciated.

thanks,
mike