Exchange newbie needs help - receiving, not delivering

Okay, go into this knowing that I'm a flop when it comes to this sort of thing - very little (read: no) experience. System is a new SBS2003 system w/ Exchange Server 2K3.
1) Exchange is receiving incoming SMTP messages - I can see them in my delivery queue.
2) My Active Directory seems to be solid - my user admin account receives the morning server performance data e-mails from the system.
3) Here's where it gets sticky - Exchange is not delivering incoming mail to the appropriate mailbox. Actually, it's not delivering it anywhere at all - it's hung in the queue.
What do I need to be looking at? It doesn't seem to be a DNS problem, (although heaven knows I've had enough of those this morning) since Exchange IS getting the mail.
I've already promised the name of my firstborn to Butch over in DNS Q&A, but my second-born....
Thanks.