Adding Printer Through Another Computer

I have a Dell Dimension 4600 that is connected to the net through a dsl modem and a wired router, I've just added a new Dell B100 and I'm trying to add the printer that is connected to my 4600, but it isn't working.

 

I've gone into the 4600 printer properties and told it to allow sharing, but when I try the printer connect wizard on the B100 and tell it to add a printer that is connected to another computer, it isn't finding it. 

 

If someone could point me in the right direction for how to do this, I'd greatly appreciate it.

 

Thanks!