This is probably about a 3 step process.
I have seen somewhere a program which will scan sheet music and make a .midi file from it...then there are .midi programs which can transpose to other keys. From this you can view or print the sheet music in the new key.

Now, if I could just remember where I saw step 1 implemented. (I will look around in favorite locations)

If someone knows a faster way, I'd be glad to see it.