IBM has a program called the Academic Initiative, which provides free of charge, course material, hands-on systems and software, to colleges and universities who want to start teaching their students about mainframes. There was also a Mainframe Programming Contest that ran just this last year, where over 700 students from the US and Canada logged into a system and performed various tasks to win prizes. The top five performers were flown out to IBM Poughkeepsie, NY for a tour of the facilities and to meet with some of the higher-ups.

Mainframes aren't going away. There's simply nothing else out there that can handle the amount of data that a mainframe can process. That's simply the way it was built. It doesn't matter if someone comes out with a 25ghz core cpu with fiber interconnects. That doesn't drive business. IBM's mainframes are built for business. Read up on GDPS, Parallel Sysplex, WLM and CICS. Comparing a "omg fast 15ghz dell server" or whatever to a mainframe is like comparing a Ferarri to a freight train. Sure, the Ferarri will smoke the train in the quarter mile, but there's no way you'd want to use one to move coal from one side of the country to the other.

If you're interested in learning the stuff, just ask around a company that uses them. While it is an entirely different world, it is fun to learn, and people are really trying to hire young mainframe system programmers now.