I just downloaded Frostwire and after I installed it, I ran it. An error message came up saying that the skin file i have seleceted dosn't exist or is invalid. It told me to either choose another file, or use the default. I haven't selected any skin files so i don't know why this error is appearing. I run Windows XP SP2, can anyone help me?

My thoughts would be to re-install it.

Another thought is to delete the FW preferences folder; How to delete your FrostWire Preferences folder

I don't have a preferences folder in my Frostwire folder. I went to exactly where you told me to, checked for hidden files and it's just not there. Maybe I need to set one up?

Use the search function but before you use it, change visibility mode of the search (see example animated image further down the page of the link I gave.) If you've opened FW once, you should have a prefs folder.