Most cards these days, even cheap ones, come with dual outputs that will allow you to use dual monitors. Simply plug the secondary monitor into the VGI output using an adaptor (usually supplied withnthe card), and with WinXP it is simplicity itself to set up. Just right-click the Desktop, choose Properties and in the settings tab, click on the second monitor and check "Extend my Windows destop to this monitor". You can have completely independent resoultions and refresh rates if you wish.

It's a lot easier than messing around with 2 graphics cards.