In Windows XP IPv6 is not nearly as good as in Vista and later, and it's also not IPv6-capable in a regular install. You have to install it yourself.

So a solution could be to have the toggle for IPv6 disabled in a new install on XP, but enabled on Vista and newer. This is how uTorrent works too as far as I know. XP is very old now, and I would be ok with doing this on that OS.