cv1 , there is a post by graylinghunter
Here, on his battery modification to an ipod nano battery. You might want to read it up first. Most importantly, measure the maximum available space with your replacement battery to ensure a fit.
Generally, you will need a soldering iron, solder wire, insulating duct tape & a fair degree of soldering skills.
Just tape up the White wire, make sure no wire from the White one is left exposed.
Next remove the old battery, and apply abit of solder to the 2 solder points on the board. Remember which of the 2 points are for the red and black wires.
Now solder the red and black wires to the original points and thats it.