I just realized tonight that I'm going to have to go back to using Outlook. Thunderbird 0.8 is apparently buggy, and this evening I suddenly stopped receiving email. After surfing around, I found that this has happened to lots of folks, although it's been fixed in the more recent nightly builds, which are less than stable. Oh well...
I had the same problem with Thunderbird. I also found that TB didn't import my Outlook Express mailing lists. I got the list title, but the list was empty. I'm currently using Outlook Express (NOT "Outlook"), but there are other non-MS mail clients out there. You may want to try Eudora (http://www.eudora.com/).