Biztalk projects dont use the assemblyinfo.cs as you are aware. it uses the btproj property instead. http://www.codeplex.com/biztalk .useful in automating daily builds etc.

Biztalk buid helper is a command line tool
It increments the version numbers of all btproj's in the vs2005 solution.
eg usage : c:>BiztalkBuildHelper.exe <solutionname.sln> <newversion>

Just pass in the Vs2005 solution name and the new version number.
It updates all the btproj version numbers to the new number