there is a time-streeching feature in Sound Forge 5 (in previous versions too), i assume its like the one acid, but i could never understand the acid one...
in SF, highlight what you want to speed up, then goto Process/Time Stretch...
basicly, if want to speed it up, shrink it, if you want it to go for longer, expand it...
you can change the may it works it out (time, bpm or percentage) so if you change it to BPM...
to do it by BPM, you have to set the inital BPM of the track, this is done in Special/Edit Tempo - here you would put 72..
then go back to the Time Stretch menu and enter the new BPM you want it to be (140)...
now this will speed the track up, without affecting the overall pitch..
BUT, you may have to play about with the MODE settings, as you may find some weired flanging, echo comes into play...
i used to use this method when making mash-ups... never doubled the BPM of a track, only went as far as say 10 bpm more...
would it not work if you were to take the bpm down to 70 and have the riff at half the speed of the beats (i dunno if that works with trance, but it works with rap samples and hardcore)
hope this helps.
Chaz.