First, plug the printer into the mac, turn it on and restart. See if it shows up.
If not go to System prefs/print and fax & click on "set up printers". Make sure the lexmark is turned on and connected to the mac before doing this.
Sii if it shows up in the next window. If not, click Add. pick USB from the drop down menu and see if it's there. If not try rendevous from the drop down and see if it shows up. In that same drop down, you might see lexmark. You can try that.
You can also go to the support section of lexmark's site and see if there's a mac driver. If you can find that, you migh get more options when printing.
Using OSX 10.3.9 on a G4