Would you be willing to post code? It can be very difficult (read: impossible) to 
diagnose problems like this without the actual program.

I can assure you it is quite possible to overflow 1GB even with a few agents, 
especially if you're building networks. One place to look first is to ensure that you 
are not creating new network links between agents that already have links; you 
would probably want to modify link strength instead of creating multiple links.