It's not a full XIP, only the MSXIPKernel folder.
SatScan provided a link in this post over at XDA:
http://forum.xda-developers.com/show...62&postcount=1
Direct link to the archive:
http://rapidshare.com/files/23680631...Build21051.RAR
CRACING also posted a link in this post, again over at XDA:
http://forum.xda-developers.com/show...3&postcount=66
Direct link to the archive:
http://www.4shared.com/file/10756780...ild_21051.html
I haven't seen any full *.RUU or payload files, so this is all that folks are sharing right now.
Best regards,
-boggsie