I assume that your two machines are connected together through a router.
Open the printers folder on the portable, right click on the lexmark, select sharing, click on share this printer, click ok.
On your main machine open printers folder, click on add printer wizard, click next, select second option, a network printer or a printer attached to another computer, click next, click browse for a printer, click next,the printer on the mobile should appear in a box, click on that, click next, printer should install, job done.
Now when you cclick on the print option on the main computer the printer on the mobile should appear in the list of available printers.
If this does not solve your problem, please reply with more information, and an alternative solution can be suggested.