ctrl-alt-f1 will get you to text mode console (f1 to f6 are the six text mode consoles), ctrl-alt-f7 wil get you back to X.
I would check for any really huge files on the machine, and for any ulimit limits that seem unusually low (ulimit -a will display them, so you can compare values when under X vs in a text mode console).
I'd also check the log files especially /var/log/messages for more precise error messages that may be relevant.
As a point of reference, I don't see this on my RH 7.1 boxes that have OpenACS 3.2.5 on them.
Is it only the postgres user that is affected, eg can you do
su brad
OK (assuming you have a user account named brad)?
