SQL 2k5: How to determine memory usage for each job

Windows server 2003 SP1. SQL server 2005 SP3. We have a number of jobs executing under SQL Agent, around 30. Every 10 to 20 days, the SQL agent starts gobbling huge amount of memory, probably following an error. When it happens, the SQL Server begins showing slow response and denies new logins. Some jobs can not start. We search the culprit job but often wind up rebooting the server to clear everything. My question is: how can I determine the memory usage for each job running under the SQL Agent? Hopefully, I can then narrow our search and find the problem. Thanks Steve