HP printer uses port 515 - cups port 631!

[dil green]

I have an HP 5si printer - managed from a pc running HP software - all fine. Small setup 4 machines, 1 printer.

Printer IP address set by router using DHCP - all fine.

Trying to print from Mac OS X 10.3.9 using Gimp-print 4.2.7/CUPS. Gimp site reports HP 5s1 fully supported - drivers present, mac printer setup proceeds ok.

On atempting to print, Mac reports attempting to contact printer on port 631, reports 'host busy' and times out.

Mac can ping printer - 192.168.1.115. Port scan of printer reports:
23 - telnet
515 - printing
9100 - hp-pdl-datastr

Do I need to change the port the printer uses (can't see a way to do this -even using full on WebJetAdmin HP software), or make Cups use port 515? (have been into cupsd.conf but dare not change anything).

I am NOT a unix head! just a poor mac user who is in too deep - have looked through all Gimp and CUPS FAQ's forums etc for relevant questions without success - can you help?

thanks in advance - Dil Green