Try using the built in Windows dialer. Type dialer into the Start search box of Windows Vsita or the Start Run box of XP. The windows Dialer should appear. Click on the Tools menu and select Connect Using, then check your TAPI driver is set in the Line drop down and close the Connect using window. Then enter a number in the number to dial box and press Enter.
If this does not result in the phone being dialed check the TAPI driver settings under the Advanced tab via Phone and Modem options in Control Panel.