So you have a ton of folks with Outlook 2003 and the are the ones looking to possibly upgrade to SBS 2011?
If so read this:
Prepare client side environment to Upgrade from Exchange 2003 to Exchange 2010 – Team blog of MCS @ Middle East and Africa – Site Home – TechNet Blogs:
As it will impact you. While Microsoft will want you to upgrade to Office 2007 or 2010, you can still use Outlook 2003 to connect to Exchange 2010.
SBS 2011 ships with Exchange 2010 sp1. So step one to make it easier to connect those Outlook 2003′s is install update rollup 2 (which includes the rollup 1 stuff)