If you go to dos prompt you can copy regedit.exe to regedit.com, you should be able to use that to get into the registry.
What you do here I'm not too sure, my best guess would be to check the following key:
HKEY_CLASSES_ROOT\exefile\shell\open\command
the REG_SZ value should be "%1" %*
If this key has been modified then I'd suggest you run a through virus check as the sircam virus modifed this key to give the symptoms you describe.
Hope this helps and good luck!