I have a saiga ak47 in 7.62 and my barrel isn't threaded but I want a muzzle brake. do I have to remove the front site just to thread the barrel?

not usually, but if it is sleeved, you will need to cut the sleeve off. Some people have found threads under the sleeves, so you may be a lucky one. Post a pic and let's see what situation you have.

Use a pipe cutter to cut off the sleeve (It clamps on and then you spin it around the barrel a few times, tighten a little more, spin a few more times, until the sleeve just falls off) I got mine for under $10 at Lowe's.

If there are threads then you don't have to do anything else.  If you don't have threads (I didn't) this is a cheap and easy kit you can use to thread it:

http://www.cncwarrior.com/ProductDetails.asp?ProductCode=25145

I installed a Damage Industries comp that had to be timed, so I used a crush washer: http://www.cncwarrior.com/ProductDetails.asp?ProductCode=23291

I had no problems doing it to my .223 version for a Phantom suppressor.