I have the same problem, too.
I have a PC with IE7, where the default printer in Windows is set as a network printer. I have set the the pdf creator printer in the print form of InfoPath 2003 as the default printer. I have try to print the form, InfoPath prints the form with the windows default network printer.
My colleauge has the IE6 installed and it works very fine.
Has anyone an idea?
Thank you in advance.