Right now, we're using PGP command line 9.0. Does anybody know if GnuPG will work? It'd be a lot cheaper.
EDIT: Theoretically, GnuPG/PGP/McAfee eBusiness Server should be able to interoperate. In practice, you pretty much just have to test to see. We did not make GnuPG work with McAfee eBusiness Server.
I've never used McAfee eBusiness Server specifically, but the entire point of GnuPG was to provide Free Software that implemented the OpenPGP spec. Unless McAfee is for some hideously obnoxious reason mandating specific ciphers, there shouldn't be a problem.
Note that if some components are going to be checking a key with PGP, and some with GnuPG, you may want to doublecheck the interoperability FAQ question for GnuPG, as you may, in fact, have to limit your cipher and compression algorithms or signature versions. That FAQ is discussing a much older version of PGP, so it may actually no longer be an issue.