welllllllllll it depends! There are so many different things you can do in windsurfing. You can just blast up and down a lake or flatwater spot and have loads fun, or you can do freestyle and have even more fun or you can sail in waves and have LOADSA fun, or you can get into the formula racing with MASSIVE boards and sails (not so much fun), etc! I find surfing helps with your balance, which is important, and also being able to read how the wave is going to break is also a plus. I enjoy windsurfing because you can get massive airs off chop or waves and then if you turn around and go the other way, you can ride some nice waves coming back in. I did notice that some of the best windsurfers have a wave style very similar to surfing, but there are still a few differences.
I'm not a good surfer, so maybe as (or if!!!) I get better at surfing, I may notice mor similarities.
But, give it a go. The feeling you get is great, and when you get good enough to ride the waves, the stoke you get is just like surfing, even though the technique (and rules) may differ. Most of all, like surfing, enjoy what you're doing at whatever stage you're at.