Q: I have an older PC with XP SP3, and a newer laptop with Vista Home Premium. They are both hooked up to the same router, but they won't see each other. According to instructions, the Vista PC should be able to see the XP PC on the "network map" once the WiFi connection is linked. But I see nothing. What do I do?
A: This can get pretty complicated. Usually, it's because the LLDP (Linked Layer Discovery Protocol) is not loaded on the XP machine. You'll need to consult Microsoft Knowledgebase KB922120. However, when you try to install it, it won't install, claiming your SP3 is newer than its files (which is wrong, actually). You'll need to extract the files by using another KB, namely KB828030 to get the files out. You should find a subdir called SP2QFE, and you should see 4 files:

rspndr.adm
rspndr.exe
rspndr.sys
rspndr.inf

You don't need the first one.

The .exe goes into C:\Windows\System32
The .sys goes into C:\Windows\System32\Drivers
The .inf goes into C:\Windows\Inf (note: it is usually hidden)

Once you got all that, open a command prompt to C:\Windows\system32
then type (without the quotes) "rspndr.exe -i"

And after a few seconds, you should see it installed. If you got an error, you probably forgot to copy the .inf file into the right location.

After this, reboot, and the Vista machine should be able to see the XP machine on the network map.