A general "square" DC brushless muffin fan will not work because it takes energy and
pulses it around a circular ring of magnetic material.

You WILL need a fan that HAS brushes before you can use it as a non efficient DC
generator.  Further, if you get a small Radio Shack hobby motor and put a "fan" on
it, it should generate enough to run a PIC after filtering and regulation.  Make sure
it is spinning in the right direction too.

Good Luck!

>>How about making a fat place in an air hose, and putting in
>>a muffin fan wired to work as a generator?
>
>Those brushless type fans in square form?