Which Direction?

I am not what you would call an experienced guitarist, so please bear with me on this one. I know that playing anywhere near Satriani or Vai is a LONG way off at best, but theirs is the kind of playing that I admire the most. My question is, what scales and modes should I be learning to point me in the right direction, and is there a site on the internet that delves into this subject in depth? Don't get me wrong, this site is fantastic, and well worth the high bandwidth subscription that I pay. However, I do find that there is not much order in the lesson content. Okay, I know that was long winded, but a little help would be appreciated.

Take care.

Maybe you should look into the "Guitar Grimoire" series of books, or even more specific books related to yer heros and learn directly from their songs and/or styles.

Which scales and modes to learn to play like Vai or Satriani? Easy...

All of them.

Try starting with the major scale and learn each mode (locrian, dorian, etc...). Learn those and to how to use them and you should have a good start in being the next Vai.