Invisible throw was done pretty much like:
(charge)->, <-, ->, Fierce+Roundhouse
There are *small* variations on it that worked too, I used them more often:
(charge)->, <-, *pause* Fierce+Roundhouse
Its a little different and it works too, but the timing is a little more difficult. When/if you did it to someone in the corner, you could continue to hold forward into them and re-do the invisible throw if you pressed Fierce+Roundhouse at the same time (think the timing of the *instant* sonic boom after Guile did his Strong throw). I have done 3&4 grabs in a row to kill (2 will dizzy and if you did it again, they stayed dizzy), but its not easy in the middle of the screen -- the corner is where you want to do it.
The later revisions of the SF2 didn't let you do the invisible throw, the "prison lock", the "re-lock" (throw them to get out of prison lock, but put them back in), Guile's standing pose or Guile's reset. All chip revisions allowed Dhalsim's invisible and Dhalsim's reset.
PM me if you want the other tricks -- I'm completely old school on this game.
vash