I'm not sure if anybody is still looking for a driver for a TP-Link TL-WN551G but I found it.
I have investigated the chipset and it turned out that TP-Link uses Atheros chipset, here is the link, where you can download the Windows XP 64 bit driver: [url]http://www.atheros.cz/download.php?atheros=AR5006EG&system=2[/url]
(hit button on the bottom of a page, it will redirect you on other page and then wait few seconds for download - it should start automatically)
Krzysztof from Poland
if anyone has a problem with downloading it - just e-mail at:
no.email.addys[at]allowed.pl and ask for driver