Well, changes from Plus 3.63 to Plus Live 4.00 are easy to find: all the language file. Translators have to start from scratch to translate it.
And the changes from 4.00 to 4.01 are very small. If you use a program to compare the lng_default.ini files of both versions, you'll quickly find the changes.
WinMerge is a great free program for that purpose.