Thanks for the links. First I tried for the easy netsh way:

C:\>netsh int ip reset reset.log
The following command was not found: int ip reset reset.log.

C:\>

# bugger

C:\>netsh
netsh>int
interface>ip
interface ip>reset

The following commands are available:

Commands in this context:
reset all      - Resets configuration.
interface ip>reset all
The following command was not found: reset all.
interface ip>do quality contol and testing
The following command was not found: do quality contol and testing
interface ip>^C

# double bugger ;-)
[download]

Oh, well so much for that. (I believe that is the approach on XP as you can't really delete TCP/IP) Next I tried the link you provided for W2K but reboots later it was still barfing. I found this M$ link which also suggests deleting a lot of registry values, so another 3 reboots later.....tada:

C:\>perl -le "print getprotobyname('tcp')"
tcpTCP6

C:\>HEAD perlmonks.org
200 OK
Connection: close
Date: Thu, 15 Jul 2004 06:37:48 GMT
Server: Apache/1.3.27
Content-Type: text/html; charset=ISO-8859-1
Client-Date: Thu, 15 Jul 2004 06:39:06 GMT
Client-Peer: 209.197.123.153:80
Client-Response-Num: 1


C:\>
[download]

All is well in the world again. Thanks very much for your help, much appreciated.