Yes - just setup all your mail accounts within a single user session. Then if you wish you can filter them into different folders.
I read several email accounts (with ThunderBird now, but with Outlook and Outlook Express before that). I don't bother to filter them though - they all go into the same Inbox except for my GMail one.
Thunderbird is easier to setup without filtering, as it automatically sorts incoming mail into separate Account Inboxes, unless you tick a box not to.