Need help regaring Modem

I am using a PCI modem. It is labelled “Diamond Multimedia systems SUP2260”. I managed to set the modems IRQ to 4. I did that because I am trying to get the modem to work in DOS mode. I loaded Windows, the drivers self installed and when I check theproperty sheet for the modem, It wont let me use it in DOS mode. The check box is faded. Yet the resource page matches the suggested resources. How do I get the modem to work both in Windows and in Dos mode? I am able to set it to IRQ’s 3, 4, 9, 10 and 11.