Windows Server 2003 Clustering, Service Pack 2 patch update

Dear Microsoft,

I need some advice on the requirement and step to do update patching service
pack 2 on windows server 2003 SP1 clustering.

I found the KB how to install service packs in a cluster and it does mention
require msdtc service? Is this a must and does it applied to service pack2?
http://support.microsoft.com/kb/174799

Because my current server does not have msdtc service install and i did try
on my test lab without install msdtc on cluster and I still able to patch
from SP1 to SP2. Please clarify out the remedy. Is there make difference with
or without the msdtc?

Thank you.