Sharing a Printer between a mac and pc?

I need to be able to print from any computer to my printer. The printer is hooked up to my HP computer. So that one can print. How can I hook my mac up wirelessly so it can also print. The modem and router are in the middle of the two (all three in separate rooms). I have an old router at my disposal. Both computers hook up to the internet from the wi fi from my router. Printer is a HP C5180 all in one. Any help would be much appreciated.