Here is the minimum you will have to do.

First, you need to determine if you can program the cutoff voltage on the ESC you currently have. If you can't program the cutoff voltage, then you will need to replace your ESC to fly Lipo's and not risk damaging them.

If you need to replace your ESC, Castle Creations makes some very good Lipo compatable ESC's, and the new Jeti ESC's (the BLUE ones, not the RED ones) are Lipo friendly too.

You will then need to determine how many Lipo cells you are going to need. Lipo's are not 1.2 volts per cell like Nimh and Nicd's. But, they are either 3.6 or 3.7 volts depending on brand.

Your cutoff voltage will need to be high enough to not let the Lipo cells drop below 2.5 volts minimal. But, be sure to read the manufactures suggestion. I have seen some cells where the minimal voltage is close to 3.0 volts.

You will need to know how many amps you will need to pull (max). Lipo's cannot supply the amps a Nicd or Nimh cell can. You will need to get the manufacturers information on the Lipo's you have to know what current they are rated too. To get a Lipo pack to supply high amp loads, you will need to set some packs up in parallel and in series. Setting the pack up in series will get you the voltage you need, where the parallel setup will get you the current capacity you will need. As an example lets say you had what would be called a 3S2P pack. This is a pack which has 3 cells in series, and has two in parallel. There is a total of 6 individual cells in this pack. Two sets of three in series and then the two sets wired in parallel with each other.

Whatever you do, before you take a jump into Lipo's, be sure to get on a good website to read all the warnings about them. They are great, but cannot take the abuse that a Nicd or Nimh can. And when Lipos are abused, they tend to burn and take planes, cars and houses with them.

Also, make sure you get a charger that is Lipo capable. Standard Nicd and Nimh chargers cannot handle the special charging needs of Lipo's. And again, check the manufacturers recommendation for charging. Abuse a Lipo during charging, and they will at best be ruined, and again, they can burn.

I hope this helps. Good Luck.