imac-wireless printer problem

bought a new iMac and new hp wireless all-in-one printer. i can't seem to set up to print wirelessly from iMac. I can print wirelessly from iPad. Can anyone help?

What model printer? And for that matter… what version of OS X?

Printer is HP estation c510 and iMac is os x 10.7.2. I called hp support and they couldn't connect me wirelessly. The printer works with USB attached. Hp suggested calling Comcast--thought it might have to do with a firewall problem on Comcast end. Comcast suggested calling hp. I have a Linksy e2000 router and a net gear wifi range extender. Two iPhones (3GS and 4s) and 2 iPads (iPad and ipad2) both print wirelessly to the printer, but iMac won't print unless USB attached. I'm wondering if my settings on iMac aren't correct.

If you go to System Preferences, then Print & Scan, is there a printer listed on the left? If not, is there anything listed if you hit the + button at the bottom, either in the "nearby" list, or via the "Add Other..." option?

Have you tried updating the firmware on the printer?
Getting Product Updates HP Photosmart eStation All-in-One Printer - C510a - HP Customer Care (United States - English)

Also make sure you have reviewed this documentation:
OS X 10.7 Lion: Installing and Using the Printer with Lion HP Photosmart eStation All-in-One Printer - C510a - HP Customer Care (United States - English)

This may sound silly but is your wireless network broadcasting its SSID (network name)? If not turn that on temporarily. Some printers seem to have a difficult time with setup if the network name is hidden. You can hide the name again when things are working properly.