Physically every woman can squirt yes. It's just different people have different ways of triggering it and some never find out how to make it happen for them whilst others just stumble on it by accident.
I actually did a bit of research on this and read quite a few different articles on it to gather what information I could as my partner said he would love if I would be able to do so for him. I found with the advice I gained I now can and I am practicing it more when masturbating to get used to it feeling more natural.
The main bit of advice that kept recurring was to relax! If you try to force it it's never going to happen.
There's a guide here http://www.lovehoney.co.uk/blog/2007/09/06/female-ejaculation-how-to-squirt/ that's got a pretty good summary of all the information I found.
The things I found that worked for me was to be extremely turned on - your partner comes in very useful here.
Already having an orgasm before you try to squirt is also something that helps for me.
Go to the toilet before you start - if you pee before you start you are less frightened that the wanting to pee sensation is what will happen and be able to relax more and recognise it for what it is.
For me I found that my g-spot doesn't tend to play ball for myself ( my partner however is another matter and he always manages to hit the spot) without the use of a toy. I found that this http://www.lovehoney.co.uk/product.cfm?p=14151 worked for me on a mid-slow rotation. The nodules on my g- spot feel amazing. There are plenty of g-spot toys, so finding one that works for you is a good idea.
I also found that if I have something inside me it is much harder to not clamp down with your muscles as you orgasm so I push to the limit (the feeling of wanting to pee and go past it) and right at the last minute/seconds pull it out and just carry on with clitoral stimulation to orgasm, this made it happen for me.
Another tidbit of information I found was this - If you find that after you have had sex and orgasmed that you need to pee urgently the likelihood is that you can squirt once you know how. The feeling of needing to pee urgently is because the liquid that would have come out with your ejacultaion has gone back up and into your bladder.
The hardest part for me is trying to hardwire my brain & body into not clamping down when I orgasm, which is what it sounds like you do the same if you're sending toys flying. Your partner will know if you do clamp down on orgasm as you'll be nearly pushing him out when it happens during sex.
Above all relax, relax, relax. It may take a lot of time and practice for it to happen so don't pressure yourself. Also don't keep going at the g-spot for too long either, it can become uncomfortable if you keep trying and trying and trying for too long. Give yourself a reasonable time limit, say 30mins max and if it hasn't happened then leave it and try again next time.
Hope you found this helpful.