Modem not Detected

[punchie12700]

I use my computer at school where we have a LAN connection. Before that I was able to connect using a dial-up. While I was at school I switched from Windoes Me to 2000 for a more stable program. Now when I come back home and try to connect by dial-up, the computer says that it doesn't detect a modem, only a LAN. Is there anyway I could add the modem back onto it? Help please.