Hi, a number of people on the board say that you cannot build muscle while on a diet (i.e. buildup you arms) and this does make sence. For me however, I have found that I have built some muscle and lost weight at the same time. Therefore I have managed to build my arms up a bit which makes me feel better as they did look rather small. Now when I say I have built them up, I am not talking big by any means, but at least you can see them now. I suspect that I will not be able to build them much as I am dieting, but certainy worth doing it though and see if it works for you.
One of the things I have learned on here is that you need to do low reps (i.e. 5-10) with quite a big weight. I tend to do about 5 sets (i.e. 5-10 reps repeated 5 times).
May not work for everyone, but seemed to make a difference to me, so worth a try.
Cheers.