high fashion photography- newbie

I have perhaps a stupid question, but what cameras and scanners do photographers use for high fashion photography and billboards?

Do they have to use really high megapixel count to blow up the images?

or do they scan a lower mp picture at really high resolution

Usually medium format cameras for fashion, which have upto 60MPs in some cameras.
You'd be surprised how little MP you need to blow up for billboards as they are designed to be seen from far away so don't need hyper-detail. Go look at one really closely.

Welcome to POTN too

Welcome to the forums. Not a stupid question at all.

Resolution and image quality are not always complimentary. It has to do with the size of the pixels as well as the number of them, and the software that processes what the sensor sees.

With that said, most stock agencies require resolutions no lower than 12 mp. Most fashion pros, canon wise, shoot with an S series camera, most probably the 1ds markIII. On the canon side, you will get everything you need from the 1Ds Mark II and the 5D as well.

Lots of pros still shoot medium format, some of which are approaching 40 mp and beyond.

No doubt, though, you can go big with a Rebel XTi, or XSi. No problem.

what camera do you own?