I agree Dave. But the thing I would say is that you have to be 100% sure that you are abiding by their terms because if you don't and they don't like it then you have got a problem. I usually don't touch other peoples images unless I have got written consent to do so using it in the manner I've intended.
Definitely ask the company if you can use their logo, get an eps file off them if they say yes, and if they're any good, they'll send over the guidelines for usage too. If you use a logo without permission and which doesn't adhere to their guidelines for use you're just going to pee people off.
i would NOT use the logo or any branding without contacting the company first. Like bigdave said, if its a stockists etc you will probably be ok anyway, BUT most companies will have branding guidelines (ie. what background should be, what resolution, etc etc)
Source: we have done a promotion where we were giving away FREE iPod Nanos (YES! costly), we bought all the products from Apple and to even feature their own product (bearing in mind it was fully paid for by us), to even mention Apples products, we had to make sure that the product picture had 100% battery charged, it was on white background, and we had to put a disclaimer which apple supplied us with etc etc.