When i did that, i used VCE.
Each checkpoint had a name. The level one checkpoint had no name because that would be pointless lol. the level two checkpoint would be named 'Checkpoint_LvlTwo' because for some reason numbers forget up for me.
the save button would basically set the variable 'PlayerCheckpoint' to 2, and then save it. the load button would check if your PlayerCheckpoint variable is 2. If true, it'd setplayertransform you to Checkpoint_LvlTwo. If false, it'd check if PlayerCheckpoint is level 3, if true, that, if true, this. and so on and so on.
http://forum.blockland.us/index.php?topic=74017.0
i'm not quite sure if S4L used those, I believe he used a script of some sort, but this works just as well
This is for V4 variables, VCE has a save/load feature in it.