Windows XP has a half brewn IPv6 support.
It's network configuration GUI lacks the possibility to add static IPv6 addresses.
It can be done on command line though, as described at http://www.twibble.org/old-content/ipv6-for-windows-xp/.
The core steps are:
# show IPv6 config
# search interface with dynamic global addresses, typically 4 or 5
# add address permamently
ipv6 -p adu 4/2001:15c0:65ff:8504::119:107