go to device manager do the "scan for hardware changes"... if the system detects the hardware then install the software...u can find device manager in the control panel
You're probably using the wrong driver. The X1550 needs the legacy driver. I assume that you're using Windows XP if you've got an old X1550. Here is a link to the correct drivers: http://www2.ati.com/drivers/10-2_legacy_xp32-64_dd_ccc.exe