I gave this a shot about 5 min after I bought my 2200. Its been a while but this is as much as I can recal.
It will not post with a P4 below 2.4. It may have been 2.2, not sure
Once I got it to post with a 2.4 I couldnt start the system off of the battery. It kept comming up with an 'Incorect Battery' warning. I had to start it on the power adapter. Once it posted on the adapter I could unplug it and it would boot the rest of the way just fine.
As for the bios flashing, I did give that a shot aswell. Either the bios was the same for both and it showed up as a 2200 in the bios anyways. Or I got an 'Incorect ROM' error, and couldnt flash it with the 2700s bios. I believe it was the latter.
I fought with this for a while thinking it may have just been a bad battery. A few weeks ago I went back to the celeron D, and its working fine now. I figure it was a power issue caused by using the P4. Drawing too much or too little gave it a messed up reading. It may work though, with a different P4. If you're comfortable ripping down a laptop give it a try and let me know how it goes.