I run mine on a Pentium II 300MHZ with 384MB RAM. I run VWS, Cobian Backup, FWINK, Webcam, Fling, Executive Disk Keeper, and a program to monitor to my inbound/outbound traffic usage (I forgot the name of it, but I think Axelvoid/Lars recommended it to me).
On the average I run about 40% processor usage with all the above programs operating at the same time. I usually restart the machine about once a month, more out of habit than necessity.
To get your VWS cpu usage down. Do not use VWS's ftp upload functions for your website. I turned off VWS's ftp and used Fling and that really cleared things for me.
Also it helps that you use a dedicated machine for your WX stuff. My WX box is for the station only. I "created" the box with a fresh clean install of Win XP and then Nothing else is installed, except what is listed above. I uninstalled/turned off all of the "cute garbage" in Win XP that I found was not needed. That really helps.