The wireless network should be pretty much the same as the wired network.
The easiest thing to do will be to statically assign each wireless
client an IP. The wireless access point also needs an IP, although
that is only really used for configuration purposes so it can be an
internal non-routable IP address.
Each wireless client needs to be manually configured with IP address,
Gateway address (probably your DSL router or possibly an IP at your
ISP, depending on your config) and DNS servers. These configuration
options should follow the same lines as your existing wired clients.
If staticly assigning wireless clients is not suitable, then DHCP
should be possible too - however this will require a DHCP server,
which either your wireless AP or DSL router probably already offer.
You will need to select a range of IP addresses that will be assigned
by DHCP, it is important that no IPs in this range are used by
statically assigned computers. The DHCP server will need to be
configured with this range, and also provided with Gateway and DNS
details to assign to DHCP clients.
If neither your Wireless AP nor DSL router have a DHCP server, then
the following application provide DHCP server functionality on