Changed home network; now can't see printer

I had a home network with a DSL router that my main computer was
connected to via Ethernet, and the main printer is hardwired to that
computer. Every other computer in the house was wireless and could use
the printer via a home network.

I now have switched to a fiberoptic internet account, and all of the
computers in the house are now wireless, because I had to put the
router where the fios line comes into the house. The main computer
with the printer is also wireless now, and the printer remains
hardwired to that computer.

Now, in spite of the fact that all of the computers are on the
Internet, they can't see each other anymore. I didn't change anything
except for changing the router (now a DLink Extreme G, before a Linksys
B); no other settings were changed. Of course, this means that the
other computers can't use the printer, either.

All computers are using Windows XP. Everything worked like a charm
before.

What do I do to try and fix this????