the should work together!
te CUSL2 has onboard Intel ATA/100 controller, while the PCI card you have must have either Promise or Highpoint controller.
Did you try to install both the drivers at once? Remove the PCI card, delete its inf files from <font color=green>c:\windows\inf\other</font color=green> and restart the machine. It should run stable with only the Intel controller.
Try the machine for a while and then install the PCI card, reset BIOS and power up. The card should be detected by Windows and it will ask for the drivers. Dont point it to the drivers and let it take it as "Other device" You should be able to work fine this way.
Now delete that "other device" from Device Manager and click on refresh. It will again detect the card and ask you for the drivers. Point it to the drivers and reboot.
Probabely it should work fine. If not, boot into safe mode and examine the IRQs.
Basically, it is a simple reinstall of the card and its drivers.
<font color=red>No system is fool-proof. Fools are Ingenious!</font color=red>