I think I may have solved the problem. The issue was obviously the ICF.
I stumbled across this solution wile searching through google.
Essentially it involves creating a entry in the ICF config to open port
445 (External Port 445, Internal Port 139). When I do this, printing is
fine.. all the symptoms are gone.

>From what I understand about these ports are what SMB uses for

Microsoft Directory Services. The port 445 is used in Windows 2k and XP
versions. Prior to these versions of Windows ports 137-139 are used. I
think care should be taken to ensure the correct precautions are taken
in order to avoid DoS attacks, worms and other nasty's when opening
this 445 port as it (and the other old ports) have been exploited in
the past.

Has anyone got any advice on this?

Cheers,

Andrew

Andrew Luke wrote:
> Further to my previous posts I have found out the following through
> testing.
>
> - Installing Windows XP Service Pack 2 seemed to resolve the issue.
> - When I uninstalled SP2 the problems returned
> - When I turn off Internet Connection Firewall on the LAN connection
> (without SP2) the issues seem to be resolved.
>
> So that begs the question, what's the ICF restricting that is causing
> the delay in sending the print job?? My testing continues! Comments
> welcome, thanks.