Just wondering. are optical drives on laptops the same standard size?

I know the exterior may be shaped aittle bit different but is it just a matter of getting a regular laptop optical drive and unscrewing any plastic casing and putting it in your new drive and slip back it back into the laptop?

I don't want to pay the company 2x the price for the same drive if I can get one off newegg.com

I hae a dell 700M and want to replace the dvd/cdrw with a DVD-+rw