If your Macromedia, uh, I mean Adobe Dreamweaver 2004 MX locks up on startup because a site that it wants to open up automatically no longer exists, here's how you go deleting your site from Dreamweaver:

1.  Sites actually exist in the Registry. So go to your RUN and open up REGEDIT.
2. Go to HKEY_CURRENT_USERSoftwareMacromediaCommon2004Sites .
3. There you will see all of the sites in Dreamweaver. Delete the site that no longer exists. I deleted the whole directory and had no issues.

If you do this and the whole thing explodes, sorry. You should probably back up everything before you do this, by using the Dreamweaver Site Backup tool . Good luck, this took me too long to figure out. Why put it in the registry!?!?