As a BI4.1 ramp-up customer, we practiced this in-place install of BI4.1 on top of BI4 SP05. It was very easy to do, as shown by the screen shots below. Note that I am not a BI administrator (just an Analyst) but it was so easy, even I could do it.
After downloading the software from the Software Distribution Center, the installation starts.
Of course all programs are closed except for this one.
Enter the CMS name and port, and the password for the Administrator and click Next
Enter the repository port and passwords
Click next to begin installation and then you wait 45 minutes to an hour
Success! Click Next.
Then I logged on to the Launchpad to run an Analysis OLAP report.
For new installations, there is a configuration wizard (more to come)