What kind of modem do you have?
My modem is an hsf but I got an Optima laptop, but it's very similar to an Aspire 1300 series, so I am not 100% sure for you.
The official site for it is:
But you have to purchase it. I think if you look around you can find the source for it and compile it. Or find older releases of it somewhere because it used to be free.
They still have a free version but it's cut down to 14.4 Kb/s. I think.
Put I know that dell has the driver for free for it's customers. I remember something like that so maybe you can find the dell version of it.
And get this they charge more for the actual driver than it cost for the modem. hehehe