I too have had problems designating a different directory for saving my downloads to other that the default. When I go to "Tools/Options/Save Directory" and choose another folder on a different partition such as "F:\My Music" I am told that it is "An Invalid Directory for Saving Files" which is puzzling as that is where all the files are that I share! However I can specify the folder "F:\My Music\Incomplete" and it is accepted! Now that makes no sense at all.

I did not have this problem in the versions of LimeWire Pro before 2.6.5 but I have the same problem in the 2.7 beta as well.