SP I promised during TechNet Gig on SQL Performance which will identify blocking spid at top of blocking chain : sp_blocker_pss80
Please follow the link below to the MS KB article containing the above SP.
Note the 'fast' parameter to improve performance by reducing the amount of extra diagnostic info returned.
http://support.microsoft.com/default.aspx?scid=kb;en-us;271509
Hope you find it useful!
M*
