From what i understand Windows vista has a anti virus all ready installed.Right
If you do have it that is what is blocking you.You can delete it and it should work fine.If you need a new anti virus than here is a link For Avg.
AVG Anti-Spyware - Reviews and free AVG Anti-Spyware downloads at Download.com
If you delete The one anti virus you got with the windows vista than limewire should work fine.Because I cant remember what it was but that Anti virus most likely is the suspect.