Have a Dell computer, need help converting to dial up internet.?

I bought a computer for my mother, it is a Dell GX250 DT 3.0 1024 80 GB Combo XPP. Is this compatible for dial up internet? I asked the sales person I bought it from, he told me all I needed was a PCI card (dial up modem). I bought that item and it is about 2 1/2 inches too big. Is this computer going to be able to able to use dial up? This is a very compact computer. Thanks for any help, I am at my wits end with this.