On Tuesday I installed a second PC, and on Wednesday I got a Crossover cable to network the two. Both computers already had a network card, so that first part was already taken care of.
Networking them was a simple case of just plugging the Crossover cable into each computer and running the Windows XP network setup wizard. Actually I was getting nothing until I discovered my main PC's network card was disabled; something I'd done two years ago when I'd built the machine, and forgotten about. It would have been nice had Windows XP informed me of this, but it appears that's asking too much. With the network card switched on though it took seconds to obtain file sharing.
Now being that my Internet connection is AOL DSL (USB) I wasn't holding out much hope for Internet sharing to work, and sure enough it didn't. The gist I got from searching online for info is that Internet sharing with DSL is simple and straightforward with most providers, with AOL being the notable exception.
One good tip I can give from pottering around is that you can connect to AOL without any of their software. Simply uninstall AOL. It's likely best to then also uninstall the modem driver and reinstall it. Then run the Network Connection Wizard and add a new connection to the Internet. For your username put your AOL email address (not your screen name - so email@example.com, not john), and for the password put your AOL password. No phone number is required because it's broadband.
Now your computer is more crap free, your hard drive has more free space, and connecting is much quicker.
Unfortunately though, I had to reinstall AOL and return to using the AOL dialer to connect because it meant I could no longer have a network. I'm figuring a lack of a router, so no way to direct the LAN/Internet packets is the cause. And just to complicate matters further, I've read that AOL doesn't like some routers.