Outlook 2003 should have copied over all your files from Outlook Express and installed itself as the default e-mail program (not "server" - the server is at your ISP). Apparently it did not full install or copy over everything. I would let it copy whatever file it wants and see if that corrects the problem. Also, check the Internet Options in Internet Explorer (Click Tools then Internet Options) Programs Tab and make sure Outlook 2003 is set as the e-mail program.
If you are still having problems, repost in the Office/MS Works software section of the forum - the forum section for support MS Office products. That is the most appropriate forum section since this is a setup/software issue, not a "networking" issue.
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