For an incredibility simple answer...use a longer lens and use Photoshop "photo-merge". You can cough out images with as many MP as you want.
This dove is 24"x30" @ 300ppi.
99% of the time, a 300mm f/2.8 lens is mounted on my 1Ds3 for everything, if not that, a 180 macro.
Just make sure your computer has sufficient RAM.