I have a 1999 chrysler 300m. I want to know what does the PO 700 code mean?

A couple of things to consider before I tell you more about this mysterious code... and everyone read on so you can answer you own questions:
1. Change your trans fluid with ONLY Chrysler 4 fluid. and change the filter.
That should be about 30 bucks if you do it. Dispose of the used fluid PROPERLY like in your local recycling center or at a local parts store equipped to handle used oils.
2. change the sensors, both input (L) and output (R).
AND
3. Clear the codes with a good OBD reader that sees and deletes Transmission errors. If you can't do that, then replacing the moon will not help.
Read similar trans issues here on FIXYA for details.
Now then:
This is a Standard Chrysler error code for transmission error codes.
(From elsewhere on FIXYA:)
"This is an informational DTC (Diagnostic Trouble Code) letting you know that it is stored in the Transmission Control Module.
Erase this DTC from the PCM after all Transmission DTC(s) have been repaired. (see what I mean?)
Using a scan tool, read the Transmission Controller DTC and refer to the Transmission Category and perform the appropriate symptom."

EATX stands for Electronic Automatic Transmission Controller.
There are four computer systems talking to each other over Chrysler proprietary bus called CCD bus.Those riding the bus are: Engine controller, transmission controller (the one we're talking about), body controller and instrument cluster.
This guy is a really smart dude who approaches the problem from a really neat perspective: http://www.kolumbus.fi/juha.niinikoski/CCD_bus/ccd_display.htm This may be more than you want.
Most everyone will tell you to take it to a dealer and have them check it out, but first try to change the fluid, and filter (and gasket), change the sensors and zero out the codes first before you spend the SAME amount of money for them to tell you you are about to be screwed. (Ask them what it costs for a basic diagnostic) I'll guess. $100. If this method fails, then okay, take it to a trans expert and tell them what you've attempted so far and that you think it is deeper than you expected. for 40-100 bucks you may hit on it WITHOUT paying all those dollars. Let me know if you can pursue this and if you have a modicum of success with this approach. I'd like to know how imaginative you can be by not saying "this is too deep" versus "I'll give it a try". Let us know.