No we cant guarantee you that it will work, but it's worth a try....
What you should do is back up the 4.8.1 installer....So if the latest version doesn't work you will have the option to get your old version back...
To do this go to your programs folder and open up the limewire folder (it should be there by default) now you will see many files right click on the installer and cut it and paste it into your documents folder....That's it, it's safe, now you can download the newer version and give it a try...
Just remember to save the new version to your programs folder....
Hopefully all the instructions I just gave you are the same in Vista as they are in XP....