You're going to need to get help on the PLT Scheme user mailing list for this one. (This is the first mailing list listed at the top of http://www.plt-scheme.org/community.html)

Tell them what operating system you're running, including the output of "uname -a", and which distribution of PLT Scheme you downloaded. Mention you need to run PLT Scheme version 372 specifically. No need to include the "-m" or "-f" options or to mention Arc, just show them the output of when you're in the bin directory and you type just "./mzscheme"

Then, once you have mzscheme working, we may be able to help with any Arc problems you have... :-)