w3wp.exe in Windows Task Manager issue

We are using asp classic on Microsoft Windows Server 2003 Web Edition. Every so often our pages get slow and even stop so we figured out that we have to go to Windows Task Manager (on the server) and in the Processes tab find w3wp.exe and 'End Process' on this and it will clear everything but we are back in business and all pages function properly especially the database driven pages.

If I watch the w3wp.exe Mem Usage stat it usually slows things down when it reaches 45,000K. It goes up and down but must gradually climb until it reaches the 45,000K range.

Can anyone explain what this is? And how I can keep this from getting in the 45,000K range so we don't have to keep manually 'End Process' on this?

Thank you very much for any info.