Help with Computer Onboard Graphics?

I have an old Emachines desktop from 2004 with Windows XP. I recently bought a new monitor to replace the CRT that I had. The only issue is that the graphics card does not support 1600x900 resolution. Highest is 1024x768. I have updated the graphics card drive which is Intel Extreme Graphics 2. Any suggestions on how to make this work without buying an external video card?