Hi.
WELCOME! You couldn't have come to a more supportive and friendly place.

I don't have FMS but I do have Rheumatoid Arthritis and gluten intolerance, so I know a little about where you are coming from. I have read a lot of articles about FMS and raw and they have all been positive, from people having their symptoms reduce significantly, to completely disappearing.
I guess for you, the only way to know for sure is to do it.

Reading this board, through all the archives and more current posts has been really helpful, and also googling RA, or in your case FMS, and raw foods. You will find so much helpful information.
I am starting off slowly because I couldn't handful a fast and big detox. I have started juicing and making green smoothies which have been very helpful. Also I am adding anti-inflammatory foods such as ginger and pineapple into my diet. I have ordered the Buotenko books (they healed themselves of asthma, diabetes, RA, thyroid and heart arrythmias, nearly all auto-immune diseases by going raw), and a good recipe book. Maybe this approach would work for you, but most people find that 100% right away is beneficial, due to the addiction most of us have to cooked food.
Good luck. I have no doubt that a raw diet is a huge step towards good and happy health!

Love ~ Michele.