Try the process suggested in step 1 above. And as suggested, if you use Vista you need to set both the installer & LW to run as Admin.
Another thing to try is, change the compatibility mode of LW, set to run as Windows 2000/NT, or if using Vista set to run as XP. To change compatibility mode, see point #5 or 6 here
Fixes for Limewire (click on blue link).