Is it possible to connect the second PC, with either a USB or Network cable, to a laptop, so that the second PC may access the Internet with the laptop's Wi-Fi capabilities?
I don't want to buy a wireless PCI card or access point for the second desktop. I don't use it enough to warrant it.
Next, configure your laptop's wireless connection to enable Internet Connection Sharing. Under Network Connections, use the wireless card's Properties panel Advanced tab and follow instructions to enable ICS. You probably do not need to let others control the shared connection since your wireless connection will be available at all times (it's not a dial-up connection). If you run into trouble with Internet Connection Sharing, search WinXP Help and Microsoft's Web site for how-to articles.
Finally, if you have to buy an Ethernet PCI card for your desktop anyway, consider that a cheap USB wireless adapter would not be much more expensive, and would probably be a better solution. The crossover cable makes sense if you already have Ethernet on both systems and really only need this connection very infrequently.