Configuring email accounts

[niter]

I am having a bit of trouble setting up my e-mail accounts on Mail as I used to have them on my PC. I have three situations that I need to be able to use. I have my .Mac account. This has no problems. Next, I have my university account. At school, this also has no problems. Last, I would like to use my university account at home. However, at home, I use Charter Pipeline. When I used to have a PC, I lived in an apt serviced by Adelphia. I had a set up for my account at school and then I had another account that checked my mail from the school server but sent it out with Adelphia's outgoing server. For some reason, when I set up a likewise configuration, Mail is balking at me. It says that I already have one account set up with my account (my unversity account) and I cannot set up another.

How can I accomplish what I want?

Thanks!