Create a new form code for user 1 and use the user's name as the form name. Select the correct printer. Save. Do the same thing for user 2. Each user will now have a form code with the default printer that is the printer they want to use. If you e-mail or PM me your e-mail address I'll send you the presentation by the Boy Wonder, Chris Powers from the last Sage Summit that explains it all.
Another option is to set up the printers on the user machines and name them the same, such as "Invoice Printer" and then make sure each user's printer is set up to print to the one they want.
Although Chris Powers' option works, if you want to change any other settings as defaults, they may not flow through like expected.
Pretty quick solution.
*Community Hub is the new name for Sage City