well the toppic says it all . I've heard of the digitech whammy that can do this and I know that boss has a pitch shifter . I've tried doing this with my gt8 but the sound is just too poor . What I wanna know is can I get it done with a good sound quality ? How ? Not talking just of single notes .

I need this to play some tunes by metallica , children of bodom , etc..

Unfortunately, no. Your only hope would be something alone the lines of the whammy, but even the best digital signal processors cannot accurately follow multiple strings at once. Even if they could, digital often has noticeable flaws in tracking even single notes, so it would sound out of pitch during different points in a song. Basically, if you want to detune and play a song, you'll have to actually detune. Besides, for that tuning, you're only dropping a whole step... not too much trouble anyways.
its possible with octave pedals BUT its not even close to perfect
actually, downtune with a pedal(in my opinion) gives a very cool tone =)
buy a tuner, you can quicly downtune to D, unless youre using a floyd rose with that tuning lock up the neck
i got tired of my signature and i no longer has one

The american fender VG stratocaster can do that i think
hehe thanks for all the replies . Yep tuning down , changing strings , good options . But if only it could be much more simpler , like pressing your foot down or just reaching for some switch ehehe that would be great but I guess it can't