Seems Phaez posted a tutorial over on Osbetas.com about how to remove ads from MSN Messanger 5.0

"Step1 - Open msnmsgr.exe with you hex editor.

Step2 - In your hex editor Search for the string "WSSh" which is connected to "}.t.j.WSSh"

Step3 - Change the "t" in "}.t.j.WSSh" to "." by changing its hex value from "74" to "EB" as the image below shows.

Step4 - Save your changes and you have an ad free MSN Messenger 5! "

Its not much but they posted a image to help with it also you can see it by clicking here