No, you do not need any special training to get started in general or legal transcription.  To have a successful and thriving home transcription business you need only two skills:

Keyboarding:  You can type at least 35 or 40 words per minute

Language skills:  You have always been a good speller and you know the basic rules of grammar
If this sounds like you, you are ready to do general and legal transcription work now!  Furthermore, if you have a background in medical terminology or if you take a medical terminology course you are well on your way to doing medical transcription.