I installed the free 1-user version of Blackberry Pro Software Express (BPS) yesterday and was quite straight forward. This was onto the same server as Exchange 2003.
Just two issues arose which stumped me for a bit.
The first was one of the Curve handsets would not activate. This was because the activation email which came from Blackberry was been caught by Outlook's junk mail filter and was the activation only works if the email is in the main inbox. Turning off the junk filter in Outlook solved that problem.