it shouldn't be. I'm running Vista Ultimate on my new Toshiba Laptop and I have Limewire 4.16.6 installed and everything is running perfectly.
Have you altered the screen resolution or anything else in Vista that might have upset Maybe you could try installing the latest non-beta edition which is 4.16.6. Get it from the official LimeWire homepage and install it after you haveuninstalled the previous version (including going into your C:\ directory and deleting any LimeWire folder from there) A good idea is to read as many of the "sticky" posts as you possibly can.
Quite often people have found solutions to their problems somewhere in these posts.
Good Luck!