...get some netbook internals as they are sure(ish) to fit and don't consume much. A netbook with cracked screen can be bought on ebay below 100$. If you can try to see the output voltage of the MBP battery and DC charger voltage. Then try to get a netbook mobo that uses that amount so you can recycle MBP's battery & charger. If you can fit regular lappy parts it's great, but they do consume more and you may have to modd the unibody to provide adequate cooling. Of course a Brazos board would be pretty awesome as with an SSD you'd have a capable entry-level laptop with MBP looks and excellent battery life. If I recall right some MSI Wind netbooks can be hackintosh-ed easier than others.
/end random thoughts
/end random thoughts