I installed WiFi at two of my uncles'. Works quite well... under a recent version of Windows. Couldn't get the PC-Card to run on an uncle's Windows 98, and I still haven't got around to compiling Linux support for any of them. The PC-Card is the WG511 from NetGear, and is said to work well with wrapper for Windows NDIS drivers (on X86, that is). Since I intended to use it on my Jornada, I decided to part with it instead and resell it to my uncle.
As for the PCI Card, this DWL-G520+ from D-Link seems quite a swell card, but its TNETW1130 chipset has no free driver for Linux (yet?). Maybe it'll work with those non-free drivers from Linuxant? Or maybe I should try the NDIS wrapper? In the meantime, I'm using a long RJ45 cable.
In any case, in the big mansion of the uncle who hosts me, with the WiFi router in a central location, I could walk around the whole house with my other uncle's iPAQ 5555, and stay connected to the Internet the whole time through though with varying degrees of signal strength. (More about that gizmo later.) On my other uncles' building, I could connect one uncle to the other through the floor, and thus allow them to share the same Internet connection. However, the signal didn't reach my aunt six floor above; Maybe I ought to try with a powerful repeater?
Oh, well. Don't forget that WiFi security through WEP is only good against unequipped laymen; with the proper equipment and a tiny bit of patience, anyone can introduce into your network: see The Unofficial 802.11 Security Web Page. Hopefully, the replacement for WEP, WPA, will be safer. Now, considering my use of a wireless keyboard, this is actually not the weakest spot in my (in)security against well-equipped wireless pirates.