I am setting up a wi-fi network in my home (using the motorola sbg900
wireless modem gateway), which will include a firewall. Is it also
important to install a firewall on my laptop(s) that will be
connecting to the network? That is, is it possible someone can do
damage to, or access information on, my laptop through my wireless
adapter (802.11g)? Thanks!

Hi bigsticks-ga,

Having a wireless gateway with builtin firewall is great, but I doubt
it will do a little to prevent someone from accessing your laptop through
your wireless adapter. Basically all that a firewall will do is to give
you control on the ports that will be enabled for a particular host on
the network.  In this particular case, it is also possible it gives you
some control on the access to your laptop through your gateway.  But
it only helps with preventing someone's access of your wireless host
through the internet.  What you need is a local IDS(Intrusion Detection
System), such as BlackIce or ZoneAlarm, in conjunction with a software
firewall on your laptop.  This will provide you with much better security
to your laptop, if the firewall on your gateway breaks, or if someone
tries to break into your laptop.  It might still be possible for a
determined hacker to access your internet through your wireless gateway.

Regards
ldavinci-ga