OS X V10.7 Lion :: Print To Windows Printer Over Internet

I spent several hours trying to get this working. I had managed to make it work like a charm last year but I had to format my mac and I lost my printers... so here we go again. 

Office setting (I am at University, that's why we all go out with out own public IPs):  

- windows XP computer connecting directly to the internet with its own IP address, we shall say 123.456.789.0

A HP laserjet 4100 printer connected to the windows XP computer, called Printer2 

- airport extreme connecting directly to the internet with its own IP address, we shall say 098.765.432.1 

- macbook connected to airport. Note that this way macbook and windows are not in the same workgroup. 

I made the windows xp share the printer and I added some exceptions to the firewall so that it would accept incoming printing jobs from the airport's IP 098.765.432.1. I downloaded the Laserjet drivers on the mac. 

And then, I tried every possible configuration to add the printer. IPP, LPD, Socket, SMB...

I tried putting as a queue just Printer2, I tried putting /printers/Printer2.. I even tried things like username:password@123.456.789.0:port... nothing worked. I just cannot manage to print, and I actually cannot even make the mac recognize the printer. 

I remember I once found out what the problem was... but that was long ago and I forgot about it..It even kept working as I switched from an old access point to the airport..

Info:
Mac OS X (10.7.3)