Not quite clear about your problem...
Am I correct in saying that the Epson has taken over as the Default Printer for both PCs but you want the HP (on the Print Server) to be the default?
And right-click the HP in each PC and setting it as the Default Printer doesn't work?
I have two XP Pro machines, peer to peer via IP, one shares a local Epson C84 on LPT1 with the other. I also have an HP LaserJet 4Plus with an MIO print server installed. When I installed the Epson (replacing a dead Cannon) it assumes default printer status when a print job is sent it's way (the HP should be default on both machines). I have deleted, installed and shared each printer in every way imaginable. Currently both printers access the HP via IP port and the remote PC accesses the Epson via //IP Address/share name.
The XP machines are virus free, have patches installed and latest drivers for each printer. The network utilizes static IP addresses for each of the computers and the laser printer. The only variable that has changed as far as I can tell is the replacement of the Cannon inkjet with the Epson C84, both on LPT1, both shared. I have searched Epson's site to no avail and have not yet gotten a satisfactory answer from Epson tech support.