Windows 7 by default uses 1) a random identifier to auto-assign IPv6 addresses, instead of IEEE 802 aka MAC addresses, and 2) assigns temporary adresses. So a system will have a different IPv6 address under Windows 7 than, e.g. under Linux. See e.g. this page. To solve this 'problem', enter the following commands:

    netsh interface ipv6 set privacy state=disabled store=active
    netsh interface ipv6 set privacy state=disabled store=persistent
    netsh interface ipv6 set global randomizeidentifiers=disabled store=active
    netsh interface ipv6 set global randomizeidentifiers=disabled store=persistent

After the obligatory reboot (it is Microsoft), you have a 'normal' stateless auto-config address, and no temporary addresses anymore