OK. I guess you are using Earthlink MailBox as your e-mail client. I know nothing about that program.
The import options that Tiger's Mail application (Mail.app) will present are:
Entourage, Outlook Express, Claris Emailer, Netscape/Mozilla, Eudora, Mail for MacOSX, Other (mbox). You need to get your e-mail into one of those formats.
If possible, it would be better to get your contacts exported in VCF format, instead of CSV as these will import easier into the Address Book application.
I actually use my iPod as an intermediary using iPod Sync to get my contacts (stored on an Exchange Server at work) in VCF format on the 'Pod and them import them on the Mac. I coulddo he same for calendar, butit's hard to keep them in sync, so I just use webmail for my calendar.
Another reason I suggested webmail as an intermediary, is that you can always access that from any machine during your transition period.
B