It's been a while since I've tinkered around with old desktops so I'm after some advise on which RAM upgrade would be compatible for a box I'm helping clean-up for a friend.

Box currently has 2x slots fulled labeled "512MB 1Rx8 PC2-4200U-444-12-D3"


I'm looking to upgrade it to a total of 4gb (2x2GB) so would this be compatible?:

http://www.pbtech.co.nz/index.php?z=p&p=MEMCRU022049&name=Crucial-2GB-Desktop-DDR2-800Mhz-DIMM-240pin-Non-EC