I had 2 laptops and a pc on a network, using XP then Vista, the only time printer from the network worked properly was when I installed windows 7 on the lot.
Doesn't help a lot I know, but I think it indicates that using XP networking a printer never really worked 100%.
I did some google searches a while back and found some good info, (which I have shredded recently due to win 7 install) on printing in a network with xp/vista, might be worth a google.