Sorry to read that you are having so much trouble. I not sure this will help, but here's all I could come up with:
RE: Multiple instances of AutoCAD
Are you opening drawings via the Windoz file manager? If so, here's a link to Autodesk NG about that:
http://discussion.autodesk.com/thread.jspa?messageID=5147025RE: Bedit
Although you can use this command to edit or create any block, its main purpose is for creating and editing dynamic blocks where its cumbersome qualities can be more appreciated.
You can still use the Refedit command for regular blocks and Xrefs.
RE: Plotting issues
Obviously the printing/plotting config is not setup right. I would check that the printer/plotter drivers are up to date. And check that the printer/plotter are installed as a Windows Printer (Control panel, Add a printer). Try creating new temporary PC3's and test them. Or copy PC3's from your coworkers that have the same OS and same AutoCAD version and use the same Printer/Plotter.
RE: Communication Center
Could be a fire wall issue. Try right clicking on the Comm Center icon and see if any options there can help. Also try shutting down AutoCAD and deleting temporary files from Internet Explorer cache.
Side note:
AutoCAD 2007 requires more computing power then 2004 and even 2006 versions. If your PC is more then say 2 or 3 years old, you may be experiences problems due to pushing it to the limit. Perhaps a hardware upgrade is due.