There are many possible reasons for this. If no other program causes lock-ups, you may try to see if any other programs are running as well as the client. Some programs early on in design can cause problems running with certain other programs due to a number of reasons...most of which would not be resolvable by this letter.

Try running the client with a clean boot with nothing (no virusscan, firewalls or anything, only "explorer" and "systray" in Task Manager), then simply open the program and wait and see. I have virtually the same system as yours, except with a Duron 850 cpu and only 256MB ram. Using GNOTELLA 0.9.9 I've had some slowing of the system, usually when I'm really going download crazy, but no lockups.

Yeah, not much help really, but worth a try...