Is this the computer just out of the shop that is downloading everything?

POP mail is an interesting protocol, especially when it comes to dealing with the only new messages bit. There is a unique ID for each message that the client maintains a list of. During the mail retrieval process the client requests a list of all the messages on the server (UIDL is the command, I believe) and then requests only the new ones through a follow-up command after comparing the list on the server to a local list. So if the local list craps out you'll have the situation you're in now, where it will download everything.

At least that's what I remember from supporting Eudora in the late 90s.

I'd start by canceling the transfer and telling Outlook to go offline. That should stop the current download. I don't think that there are any settings in Outlook 2007 to tell it to only download messages from NN days ago. Perhaps you can make a new folder, move everything out of your inbox into the temp folder, let it do the download, delete everything that is old in the new inbox and then merge it all back together. You'll have to deal with the 4 hour download, but at least you avoid the dupes. If you have rules and whatnot filtering messages into folders it will be much harder. In that case you could set up a new PST, let it download and then add the old PST back in to your Outlook profile and merge manually that way.

If you can get away from POP3 you'll be a much happier user. IMAP is a way better protocol, especially for someone with multiple computers in use.