I wrote a blog regarding issues i was having with that:

http://www.sqlservercentral.com/blogs/christaylor/archive/2009/05/04/sql-server-cpu-s-at-100-anyone-checked-the-vas-virtual-address-space.aspx

I have however just realised i've negated to include in the blog the fact that we got a lot of CXPacket wait types when we hit this issue.