file lookups are based on the OS and in some cases that can be slow which can cause the Winamp UI (dependent upon the skin) to either lockup or act slow as you're describing.
as for your last comment, if that plug-in is present, then it can cause a slow down since it's causing Winamp to do artwork lookups which if it's a massive image, will be slow.
if anything, i think there's probably something wrong in general with your install or it's just normal if you've got 1000x1000+ images in the files and is probably time you provide an info report of your Winamp install (see
http://forums.winamp.com/showthread....161361#plugins and attach the report to this thread).