wow !!!! your using 100% physical memory ?is that after you start the PC ?
if it is then go to Start > run > msconfig > start-up
in start up remove/kill as many apps as possible at start up.....
By the sounds of it , you have a shed load of apps runnning in the background.......
You can buy 1GB of memory , and still have the same problem if you have so much stuff running in the background......
I have 512MB ... and the only things running in the background is NAV2002 ... email .... SETI....