Cluster Groups for BizTalk and SSO

I have a question about setting up a clustered BizTalk 2006 environment
using 
MSCS. I have 4 Win2003 servers - 2 for the BizTalk 2006 tier and 2 for the

SQL Server 2005 tier. According to the do***ent "Installing and
Configuring 
BizTalk Server 2006 in a Multiple-Computer Environment" 
(http://www.microsoft.com/downloads/details.aspx?FamilyID=B273269C-97E0-411D-8849-5A8070698E4A&displaylang=en),

one cluster group should be created for BizTalk and another cluster group 
should be created for SSO.

However, another do***ent indicates that both BizTalk and SSO must be part

of the same cluster group (see the last sentence in the first section). 
(http://www.microsoft.com/technet/prodtechnol/biztalk/2006/library/bts06clustering/4daea7c6-7d26-440c-a2a0-fa018a25b2b3.mspx?mfr=true)

Will BizTalk and SSO work properly in separate cluster groups or must they

be part of the same cluster group?

Thanks