is there anyway to undo your talent choices?

On PC, you can with the command console. On PS3/360, gotta make a new character.

Without mods this is not possible, except for reloading an earlier save.

any idea what the code is for that

It might be possible on the PC through console commands or mods that deal in that.

If you're on consoles: sorry, but you're S.O.L.

http://elderscrolls.wikia.com/wiki/Console_Commands_(Skyrim)#player.addperk_.3Cvariable.3E
http://elderscrolls.wikia.com/wiki/Console_Commands_(Skyrim)#player.removeperk_.3Cvariable.3E
http://elderscrolls.wikia.com/wiki/Console_Perk_Codes_(Skyrim)

You can use the remove perk code to remove any perk you didn't want, but you won't get the perk point back. So then you need to use the add perk code to give you the one you want instead.

Or the UESP has this and other information as well.

http://www.uesp.net/wiki/Skyrim:Skyrim

thanks all