Thank you both for your help
. Part of the problem was that I wasn't doing the install (a system administrator was) and therefore couldn't answer all your questions. Here's what ended up working (once I got administrator access):
switcher mpi = lam-7.0
./install.com gnu xxlarge M
That's all there was to it. I think the "two lams" the admin was referring to were /opt/lam-7.0 and /opt/lam-with-gm-7.0. Also, he had mpi set to mpich.