modem problem

I have just got a second computer from a friend,its compaq deskpro 5133
I`ve formatted it, reloaded windows98
But it cant detect the modem.
The trouble is that i dont have any installation disks and i dont know what make it is.
The only thing i know is that it has a conexant chip with no.RH56D/SP-PCI on it.
Any help would be much appreciated.