I tried 7zip , it doesn't see the control.tar.gz or debian-binary, just the data.tar
WinRAR doesn't seem to understand .deb files either. Mine is registered but I thought the basic version is the same, it just nags a bit.
I'll try some of the other suggestions next...

-edit-
okay PeaZip has the same issue, wtf...

IZArc and File Roller (on Ubuntu) can open the deb and tar files fine but can't add anything back to them because all the compressed files are in some stupid "." subfolder

ignoring that problem, neither IZArc or File Roller will let me add files to a .deb
IZArc lets me create a deb but actually creates a zip file... argggh

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decided to try this script: http://ubuntuforums.org/showthread.php?t=636724