Hi folks,
My arduino prokect is finished. Now I want to use a rechargeable battery or extrernal power.
I also want to recharge the battery by using the same plug the external power uses.
All in all I want it to work like my chellphone. When I plug in external power it recharges and powers the board.
how I that done? I realy am clueless on that one.
Thanks in advance 
Have a look at this:
http://proto-pic.co.uk/products/LiPoly-Charger-%252d-Single-Cell-3.7-%252d-7V-Input.html
It's based on the MAX1555 chip which sounds like it could be what you're after.
Good luck
The charger from sparkfun is great, I have one, but it won't do what you're looking for if you want power while charging. It's also not a shield and is designed to work standalone.
If you want a "plug and play" solution LiquidWare's Lithium Backpack might be just the ticket :
http://www.liquidware.com/shop/show/BP/Lithium+Backpack
I have one and am getting ready to use it right now.