iMovie refused to run on the iPad 1 because the RAM was only 256. iMovie only ran on the iPhone 4, because it had 512 megabytes of RAM.
We can safely conclude that the iPad 2 has at least 512 megabytes of RAM, because iMovie requires that much.
I daresay RAM will be increased to 1 gigabyte (if not already) when the retina display for iPad debuts. 4x resolution requires more RAM, as I've noticed on the iPod Touch 4.
RAM not mentioned (so it's probably not increased).