If that is all you do, upgrading the RAM will help extend the life of your system a little longer.
But sooner or later, you will need a new system. And that probably will be when you get tired of the long boot times as the OS loads, then the antivirus software loads, and the firewall loads, and the ...
http://www.intel.com/support/mothe [...] 015834.htm your motherboard will support 2 Gbt of memory at it's max. As the board only supports PC2100 (DDR266) the price for a relatively good boost will actually be cheap.