First make sure you aren't looking at a copy in your browser cache. Browse to your home page and then press Ctrl-R if your using Firefox or the F5 key if using Internet Explorer.
Next check the list of files in your web directory. The web server software looks for files starting with the word 'index' and besides index.htm there could be index.html, index.pl index.php etc. Though if it doesn't find an 'index' file it will display a list of the files and directories instead. So one thing you might want to do is delete or rename all the 'index' files until you see the listing, and then only upload your index.htm file.
If its still not working make sure you are uploading to the web directory (DreamHost Web Panel -> Domains -> Manage Domains, 'Edit' the domain and check) or you may have an .htaccess file that modifies what the web server does from an initial setup.
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