
If you can enable "PPPoE passthrough" on your ADSL Access Device you may be able to run a PPPoE client from your desktop without affecting the other hosts on your LAN.
Mac OSX ignores ICMPv6 RAs via PPPoE by default. The OSX kernel is known to panic when an RA is received and "accept_ra" is enabled.
You may be able to configure a third party DHCPv6 client to obtain an address via Prefix Delegation.
Windows XP does not support IPv6 via the in built PPPoE client. Third party clients may work.