PaintShop Pro / Photoshop / Microsoft Paint (if you use that, I'll give you some credit
) for the visuals; I guess you might be able to use VB4 for the internals, but don't hold me to that -- I don't even know how you would go about doing that. Probably the easiest language to program an equalizer plugin for Winamp would be C++. If you've never coded before... good luck.
Another place that might be worth looking at woudl be the Nullsoft Developers Network:
They might have something there that will help you on your way.