The 6to4 adapter, as in "six to four," is a transition mechanism used to migrate from Internet Protocol Version 4 (IPv4) to Internet Protocol Version 6 (IPv6). 6to4 is a IPv6-to-IPv4 conversion layer. 6to4 allows IPv6 packets of addresses to be contained within IPv4 packets for these to transmit successfully over IPv4 networks.
It is not uncommon for the "6T04 Adapter" to show up as a conflict in Microsoft Windows Vista device manager (mmc). They can be safely removed without issue for most users. If after removal, the desktop is no longer able to access the Internet, simple add hardware detection wizard to rediscover.