For managing virtual memory, I’d recommend setting it so that the minimum is 1.5x of the physical memory, and maximum is 2x.
Example: If there is 512MB of RAM installed, the minimum pagefile should be 768MB and the maximum 1GB
For cleaning up startup items, I always bypass MSCONFIG, and go to the key in the registry that MSCONFIG is pulling from:
If you delete items from in there, they no longer start with Windows, and you can still have a “Normal” startup as far as the MSCONFIG tool is concerned.
For troubleshooting performance, a good tool to begin using is Sysinternal’s Process Explorer (now Microsoft Process Explorer). Just google that and start using it – you’ll be suprised how much it has to offer.