The product bulletin on 12.1(11b)EX1 for Supervisor Engines (see http://www.cisco.com/en/US/products/hw/routers/ps368/prod_bulletin09186a0080092390.html) reports adding support for 802.1q in 802.1q (802.1q Tag Stacking).
The release notes for 12.2 (http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/release/notes/ol_14271.html) report that the WS-X6548-GE-TX, WS-X6548V-GE-TX WS-X6148-GE-TX, WS-X6148V-GE-TX, and WS-X6148-GE-45AF cards do not support 802.1Q tunneling. There is no such caveat for the various 10 GE cards (WS-X6502, -6704, -6708 and -6716) so you should be fine.
Configuration of the feature is covered in http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/l2pt.html
Hope this helps. Please rate the post if it does.
