Horgy,
I did the 757 with Jetlinx & found it to be a fantastic course. I also used FS2004 with the 75 add-on and also a 757-200 dvd from Flightstore about an airtours flight.
Both these things made me feel much more at home in the sim, although they in no way prepare you for the real thing. However, you spend a lot less time looking for switches, etc because of your prep. Jetlinx run the course like a virtual airline, so you are expected to learn their SOP's which makes it a lot more realistic.
One word of caution though - the MCC is a non technical course - it's about working together to fly an aircraft, not how well you know the 757. You may swat up on everything there is to know about the 757, but if you can't work with another pilot to fly it, there's no point.
If you want more info on Jetlinx, PM me.
DW.