I suggest you take a look at the white paper: "Troubleshooting Performance Problems in SQL Server 2005". The section on memory tuning /analysis is very good.

Also, using the -g512 startup switch isn't really a fix. It's just a band-aid on the problem. Your issue is that you have either 1)not enough virtual memory or 2) too fragmented virtual memory. or both.

A case with PSS on memory tuning may be in order also.

Thanks.