Unless you actually use Windows Search to find files, I recommend running services.msc and setting Windows Search to Manual or Disabled to ensure that Windows hasn't decided that it wants to index your file system anyway.

Though the easier way to diagnose this would be to watch the services running with Windows Task Manager and see what it's doing when the drive starts thrashing.

If you want to check the size of your virtual memory cache, go to Control Panel -> System -> Advanced System Settings (on the sidebar) -> Performance -> Settings -> Advanced tab. Under the Virtual Memory subsection the "Total paging file size for all drives" is how much virtual memory is currently allocated for use. By default Windows controls this and will adjust it accordingly. You may want to hit Change and tweak a few things. First of all, if you have multiple physical hard drives in your system, change the page file location to a drive that does not have Windows or Poser installed on it. And given free reign, Windows used to allocate more virtual memory than it actually needed, so you may want to put a set value or range of how much you want it to use. Since you've got 3GB already, another 3-4GB of virtual memory should be more than enough.