Register at the hotel by calling (708) 827-5131. When you register, tell them you are from the MPI Forum to get the special rate (around $95).
When you arrive at the airport, make your way to Terminal 4 (follow signs). There a red bus from the Ramada Hotel stops every 15 minutes. The Hotel is about five minutes away.
If you have any problems, send mail to lusk@mcs.anl.gov or call me at (708) 252-7852.
Rusty Lusk