Thanks to all of you for your replies. Thanks to a payroll glitch (my paycheck yesterday was a whopping $45, which is short, oh, about 40 hours), it will be a few more weeks before I can spring for the wireless router and wireless card for the laptop. So for the time being I'll just put another NIC in the desktop and share the connection with the laptop via ethernet. I've set up that kind of configuration using mandrake at my office, so it should be easy to replicate here at home (using shorewall; any comments on shorewall's security?).
Treeg, your comments about smoothwall are sort of intriguing. Is there a way to identify which routers run smoothwall? If I can get my hands on a cheap old PC, I'd be really happy to run smoothwall as a dedicated router, per static's suggestion. The only problem there is that I seem to accumulate hardware pretty rapidly: cable model -> dedicated firewall -> switch -?-> wireless access point. Static, do you have any pointers to information on security of NAT gateway/routers versus a dedicated firewall? I trust you when you say they're not as strong as a true firewall, but on what specific grounds are they inadequate?
Thanks again, everybody.