hi passtheflask!
Cool name btw (what's in the flask then? got me curious now!

). Great that you're considering going vegan, I know it's the best thing I've ever done! However, "just" switching to a vegan diet won't let you lose much weight as such, you'll need a
healthy vegan diet! That includes a variety of fruit and veg, beans, pulses, grains, tofu etc, and drinking enough fluids, preferably water. That's the very basics, I'm sure many other people will be happy to throw in their 2p's worth when it comes to that. I wouldn't know whether
all soya protein mixtures are vegan. I'm in the UK and I use Holland and Barretts, which isn't particularly nice, but vegan, and if it's at all available Twin Lab, which is a lot nicer and vegan too. I mix them with fruit (juice), soya milk and yoghurt and throw in some seeds for my omega fats. Whizz it in blender and there you go. I'm just wondering why you'd want to use protein shakes in particular? If you're worried about protein intake, there are plenty of foods which are rich enough in protein, without having to take shakes. Don't get me wrong, nothing against shakes, just wondering. Protein shakes as such won't make you bulk up either. It really is a myth that, as soon as you start working out and taking stuff like protein shakes, you'll bulk up like a balloon, unless you're very lucky - or in your case, unlucky. It takes a helluva lot of work to become big - ask any of the weightlifters on this site!
Personally I don't think that protein shakes as such would be particularly helpful with losing weight; the only advantage I can think of is that they fill you up (I sometimes have one as an evening meal, a litre of shake after a workout does the job for me!). But it might not be the best thing if you want to lose weight. Check the packaging to see how many calories an average serving contains, that should give you some idea.
I'm sure you know that the basis for losing weight is dead simple: your calorie expenditure should be more than your intake. So having an active life, with regular exercise, combined with a varied, lowfat diet should give you the desired results. If you eat lots of fresh fruit and veg they will fill you up, without giving you too many calories.
Personally, I'm very sloppy with taking any supplements, just can't be asked and I still seem to be healthy for it, so it doesn't bother me, but many people supplement their diet with a multivitamin (just check and make sure it's suitable for vegans!).
Right, that was way more than my 2p's worth, hope that you're getting some more input - but I'm sure you will!
See ya,
Malcolms Billy