While we're on the topic of pc's

Can anyone helpe figure out how to add a second monitor to my netbook? I have an Acer netbook with XP as the OS. What I am trying to do is hook up my Sony LCD monitor so I have aa bigger screen to work from. I have plugged the monitor into my computer, went to display and checked the box to put the 2nd monito to "extend my windows to this monitor" (that's the only choice i have). The second monitor came up but only with the Acer wallpaper background. When I move my currser all the way to the right of the screen on my pc it will show up on the second monitor after it can no longer be seen on the pc's monitor. It's as if the second monitor is only an extension to the pc monitor and I can not get it to function with the same info that is on my pc's monitor. Any ideas on how to make the second monitor act as the primary or in tandem with it. When I check the "make this my default monitor box" it will just shut down the second monitor and will not allow the selection to be done?
Thanks in advance and any help will be appreciated.