SunnyD: There is a standard-looking scrollbar built-in to mIRC. You just never see it used because its use is rather limited as compared to the other features of standard dialogs.
anthony1293: A nice basic mp3 script, looks pretty good. However, might I suggest that rather than using $sfile(), use $msfile() for selecting files? That way, someone could select a single file, or multiple files (say they want MOST of the songs in a directory, but not ALL of them.)
Also, take a look at your writing routine for $sdir(). While no, there is nothing wrong with it, you have noticed that there is a substantial lag when writing a lot of files to your playlist? I myself would suggest that, rather than using a regular write, you /fopen the playlist file, /fwrite all your finds with $sdir(), and then /fclose when done. When I made the switch from regular write to this, there was almost no lag in my MP3 script when creating a playlist (and it creates a second list for song names). It went from maybe 50-65 seconds on my PC to create a ~500 song list (for both), to about 15-20.