If you are trying to use Apple's AirPrint for your wireless Wi-Fi printing then you need a compatible printer - apparently HP is the only ones that are in this category at the moment - check HERE at the bottom for a list -
So, the first question is 'what' printer are you trying to use for this function?
Second, there are a number of other threads discussing this very issue - might want to try a search - other apps are available that can provide printing from the iPad to a non-HP printer - Tim recently has recommended FingerPrint (check HERE) - $10 or less and seems like a good solution - I'm about to give the program a try on my Windows XP computer w/ a Canon Pixma printer attached - good luck!