I checked the Apple site and there is no spec on how much space images take up. On my iPod they take up 660k each. Apple lists how many images fit on an iPhone and iPod but nothing for the iPad.
It's totally relative to how you set the sync iirc. If you go to the screen size, probably not all that much more than what you see on the iphone/touch - Hmm perhaps it auto resizes - I thought you could set the sync size but it appears I was mistaken. Haven't ever really used that feature on the iphone but will be on the ipad!
well, one nice thing I have noticed is that the images are optimized for the iPad during the sync process.... This is HUGE for me as I shoot with a Canon 5D Mark II 21 megapixel camera and the files are really big. This should help cut down on the space needed to store my jpegs