Today, I have done an OS downgrade project (Vista to XP) on a built up compact PC for my client.

Everything went smoothly... dual boot working OK,  motherboard drivers OK, sound card OK, wifi O... ugh NOT WORKING!!!! Btw, the adapter is a Lite-On 802.11 b/g wireless network adapter

So I went to that compact PC manufacturer website looking for correct driver. Unfortunately, they don't support Windows XP, so no XP driver to download. Lite On not listing any driver for wireless network adapter.

Google... Google... Google... ahhh.... could not imagine live without one.

After countless hour fiddling with drivers from several websites, I nearly gave up.
Then I realized how stoopid I am...

Ugh, restart the machine, go to Vista, see the device manager .... ta da!!! The wireless adapter is not using a Lite-On driver. It uses a Ralink driver. Ah... beautyfull!

The rest is eazy... go to the Ralink site and find the correct driver (do I even need to say that?).
EDIT : Link expired, try this one (thanks to ckan):

(Big thanks to Ralink)