How to join 2 different network segments

[Barry Yu]

In the office there is already an existing LAN with 6 desktop machine 1 
dns server / dhcp server / gateway, ip address range 10.1.10.110 ~ 
10.1.10.240, connection of entire LAN is by cable with a switch box, 
every machine is working fine.
Now I want to add a Linksys router WRT54G in the office to enable 2 more 
laptops ( or more than 2) equipped with built-in wireless network card 
for the network, how ever, these laptops can only go to the Internet and 
communicate with other wireless laptop in the same wireless group (Same 
ssid), but can't communicate with those wired desktops, the way I 
connect the wireless router is : With a cat 5 cable one end connects 
from the Internet port of router and the other end goes to one of the 
port in the switch box ( Where all desktops are connected). I would 
imagin that unless all of the desktop each adds a wireless network card 
to enable them to join the wireless network group, otherwise 2 different 
network segments can't communicate at all - Can anyone give some ideas 
how to make the wireless group to join the wired group?