This method has a few limitations though, you can only use exactly 5 letters, so try the following method from tweakersguide.com (but it's in German so here's my rough translation)
First of all you will need to download a exe editor - Resource Hacker and Hacker 2.0 are avaliable from www.downloads.com and are adequate for the task in hand.
The first 3 steps stop the file we are going to tamper with from being restored automatically when windows restarts
1) with notepad or a text editor open the file c:\windows\system32\restore\filelist.xml (you might need to change it's properites from read only first by right clicking on the file and selecting properties, then remove the tich from the read only checkbox)
2) add the following line to the first section to exclude explorer.exe from the protected file list
3) save the file (and apply the read only properties back if you wish)
The next 2 steps actually modify the explorer.exe file that is the windows shell so back it up first if you are uncertain what you are doing (to back up the file, open a cmd window and type -
copy c:\windows\explorer.exe c:\windows\explorer.bak)
4) Open the file c:\windows\explorer.exe with your exe editor and edit the text in following lines
String Table > 37 > 1033
String Table > 38 > 1033
You just edit the text inside the "Start" to what ever you want and compile if necessary (depends on your exe editor - you will if you use ResHack)
5) save the file as (file > save as) explorer.xp (back up this file to another disk if you want to save a bit of hassle after you recover the machine next time)
Now you need to copy the file you've modified best way I've found to do this is to boot to safe mode command prompt although it's been suggested that you can stop the explorer.exe process with Task Manager, copy the fie in a cmd prompt then restart the process again - that worked for me but the origional returned after a restart. The next 3 steps describe how you copy the file
6) restart the machine and start tapping F8 to get the start menu - choose safe mode with command prompt
7) log on as Administrator and you'll be presented with a cmd prompt
8) To copy the modified file just type
copy c:\windows\explorer.xp c:\windows\explorer.exe
assuming that's where you saved it to with your exe editor)
9) Restart Machine and VOILA!
If anyone wants to tidy the tweak up a bit feel free.
Is there an easier way to do it? I almost messed up my comp trying that. Windows said explorer.exe wasn't a win32 app and couldn't boot in! I fixed it by restoring the files from the disc. Thx Lonman for that! He told me about this restoring files command luckily. So is there an easier way to do it?
well, thats the best way to do it..just boot up in safe mode with command promt and replace the explorer.exe. there's an app out there that renames the button, but that goes back to normal every time u boot the machine. go to webattack.com and do a search for startbutton renamer....