Thanks for all the replies lads.
I've tried the steps above, and I get an error when I tick "Share this printer" and OK or Apply:
"Printer settings could not be saved. Operation could not be completed (error 0x000006d9)."
Googling for this error has brought me to a number of pages that say Windows Firewall should be on in order to share printers. Sure enough, Windows Firewall is not running on my server. But I can't start it, it's set to automatic and doesn't run. Starting it manually ends up with a "Windows could not start the Windows Firewall on Local Computer. For more information, review the System Event Log. If this is a non-Microsoft service, contact the service vendor, and refer to service-specific error code 5."
Looking at the System event log I'm no smarted, it reports "The Windows Firewall service terminated with service-specific error Access is denied.."
Trying to find any info on Windows Firewall just brings up tons of sites with people having problems with XP or Vista, none of it has any relevance.
I'm seriously considering reinstalling. Can anyone check if their Windows Firewall service is running?
It started reporting errors in the log about the firewall service (I haven't noticed) since the 2nd of September. I haven't installed any updates or software on that date

And is it worth it trying to "repair in place" ?