Coca-Cola said:
Airport extreme is what you must have.
If wireless printing is all he wants, then a standard wireless router is all he needs.
The cheapest way to go would be to buy a $40 802.11g router. Many to choose from at this price range. Plug the printer into the eMac (via USB) and "share" it to the network. The iBook will be able to find the printer as long as you leave the eMac on.
The next level up would be to buy an Airport (or Airport extreme card) for your eMac. Set up an "ad-hoc" network between the iBook and eMac. Then do the same as above. This will cost you about $80-$100 for the Airport card.
Next option would be to buy a $200 Airport Extreme Basestation. Make sure the printer is compatible with the AEBS's printer sharing function. You would plug your eMac into the AEBS. The iBook will connect wirelessly. This gives you the benefit of being able to share the printer without needing to keep the eMac on all of the time.
A similar option to the one above would be to get an Airport Express. However, you would need to get an Airport card for the eMac since the AExp doesn't have an ethernet port for the eMac to connect to. This would be $130+$80 = $210 (or $230 if you need the Airport Extreme card for the eMac).
Keyspan makes a USB server that retails for $130 that can be added to a regular router (or wireless router). It'll enable you to share the printer with any computer connected to the network. However, it's not a print server in the traditional sense. Each computer will need to "lease" the printer and "release" it when finished. The advantage is that you can hook-up scanners, USB hard drives, and multifunction printers as well. Add this to a $40 router and your set-up costs $170.
Every option except the 2nd will allow you to easily share a broadband internet connection. You can do it with the 2nd option, but you'd have to hook up the cable (or DSL) modem to the eMac and share the internet connection to the iBook. It'll work, but the 1st option is cheaper and easier.
I hope this isn't too overwhelming.