[Begin Shameless Plug] Hey, check out our sister site,
DigitalMediaThoughts.
It's a great place to post questions like this (that have nothing to do with PocketPCs). :wink: [/End Shameless Plug]
On to your question:
Nvidia's
nview drivers allow you to just that: extend your entire desktop across two screens, task bar included. I picked up a GeForce FX5200 for pretty cheap (like $60) at a brick-and-mortar that works great with two monitors. Of course, go for something better if you're into gaming or other graphically-intensive applications...