fetchmail and mbox migration

[darkweb4]

I might be inheriting an older compaq from my mother when I
get her new computer built.  I was thinking that I could use
it as a mail server.  I have dial up.  Will I be able to
have a mail server without a persistant IP address?  (and
yes, i know that i'd better check with my ISP first about
policy on personal mail servers)  If not, i'd at least like
to use fetchmail or something similar to download my email
to a central location.  However, I already have 30-40 megs
stored in mbox format on another computer.  How would I go
about migrating the existing email into whatever format the
mail server/fetchmail will use?  Also, what are some
recomendations for different mail servers?

Thanks

Tim