Music library management issues

Yeah, I have got a problem. I've got a significant number of legal mp3's (in case the RIAA is reading) that I transferred to my laptop from an older computer. The problem is that I have a large number of duplicates and missing files. Nothing I can do about the missing files but the duplicates now are a tricky issue. I could just live with it, but I have a significant amount of hard drive space tied up in unnecessary MP3's and no easy method for tracking down which songs I can be rid of. If anybody knows of any handy file utilities I can use or Windows commands I can use I'd be much obliged.