Here's a little more detailed version of the tutorial for making a series charging setup. It was made by BrianG from RC-Monster forums, who is the creator/author of the ScriptAsylum RC Calculator site.

http://www.rc-monster.com/forum/showthread.php?t=9881

I use this method for charging my packs, since all my vehicles use a 2x2S lipo setup. I already had the main lead series adapter for running the vehicles, just needed to make the balance adapter. I find this method works very well for my needs because all my packs are bought and run in pairs, so their discharge states, capacity, age, etc. are always matched. If you plan on charging packs that are not so evenly matched the parallel method may be a better option.

Here is a pic of a 2x2S 5000mah setup ready to connect to the charger. As far as the charger is concerned, it's the same as a 4S 5000mah lipo (the circuit schematics would be identical). You can't see it, but on the adapter I have the 2S balance connectors marked + and - so I remember which pack to connect them to. Based on the connection of the main lead series adapter the upper pack is more positive and the lower pack more negative.