Problem with new installation of 10.5 & Mail.

I've just upgraded to 10.5 (early G% with no camera) but Mail didn't load my old mail boxes so I can't read emails I need. 1) Can I get Mail to load them or 2) where on my Mac are they kept so I can deal with them, please?
Thanks for any help!

 

Thanks, No. I have upgraded to 10.5 (from 10.3), at least that's what About this Mac, tells me. Mail works fine, but when I opened it there were none of the mailboxes that my old Mail had. I had them for ebay, paypal, & 10 others. As I can't see them I can't read even the emails I had before upgrading. Does upgrading delete old mailboxes? If so I'm stumped & a lot if info I want has gone. Firefox has all my old bookmarks.....