TPATERSON, Your computer needs Windows 7 drivers, specifically the video card drivers. This would allow you to change the resolution. If the computer you have is the Dimension 3000 there are no Windows 7 drivers. 
My 3000 was supplied with XP;  I eventually changed to Linux when MS threatened to withdraw support for XP.  I've now replaced Linux with Windows 7 Home.The only(?) problem so far is the screen resolution. The resolution is stuck on 640x480 with no option to change; thescreen is shown as Generic PnP Monitor (standard VGA etc).  The screen is a Dell 15" lcd which came with 3000.  The hardware description in Device Manager is MONITOR\DELA00B. Does anyone have any suggestions on how to change the resolution? tp
Screen Resolution