You have come across just the person to ask. (Or actually, I've come across the question. But still.)

What you're looking for is the iDroid project. 

It's available for iPhone 2g, iPhone 3g, and the  iPod touch 1g; it's a WIP for everything else (from iPad to iPhone to Apple TV to iPod touch).

Here's the installation guide:

http://www.idroidproject.org/wiki/Installing_iDroid_(Bootlace)

Here's the basic summary:

1. Jailbreak your device using redsn0w.

2. Open Cydia and install Bootlace.

3. Open Bootlace and go to the OpeniBoot tab. Let it install OpeniBoot.

4. Then go to the iDroid tab and install iDroid.

Be sure to read the whole guide first, though; there are bits I didn't include in my summary like this:

Also, touch the (i) on the upper right corner to extract the Multitouch Firmware and Download the WiFi Firmware. You have to touch those buttons for the firmware.

(Because I'm not entirely sure what they mean.)

Have fun!

Why do you want Android on iPhone?

Thanks, Gibbster