First you need a tool called "Resource Hacker". This free program allows you to change resources in any .exe file such as "Explorer.exe", which includes the [Start] button's Label. You can visit Download.com and search there for "Resource Hacker".
After you download it, follow the guide here:
Step 1:
A - Run "Resource Hacker" and open the file "%windir%\Explorer.exe".
B - You see a Tree of all Resources in this file, expand the "String Table"
C...
