Imac Dial-up Connection Plz

My gf has an IMAC.. I believe its a G3 (pretty old) one of those all in one green moniter-lookin deals. I got OS X for her and since she has been at GSU shes been on the network. Now that she is home she needs to connect via dialup but for some reason the thing wont let me make an "internal modem dial-up connection" its like it doesnt recognize there is a modem.. the option is grayed out when I try to make a new connection .. the only options I have are for setting up a network connection.. I have tried everything I can think of but alas.. I'm a Microsoft Windows kinda guy.. not used to the IMAC end of things.. Can anyone help plz?!? Thanks

Mike