When it comes to adding RAM, Lenovo's IdeaPad S10 netbook is incredibly easy to upgrade. All you need is a DDR2 PC5300 SODIMM in 512MB, 1GB, or 2GB capacity, a mini philip's head screwdriver, and five minutes of spare time.
Before you go buying a new SODIMM, you should be aware that the S10 has 512MB soldered onto the motherboard and only one DIMM slot. If your S10 comes with more than 512MB preinstalled, chances are that there's already a DIMM sitting in the slot and you will have to remove it if you choose to upgrade.
The motherboard also cannot recognize more than 2GB in total, including the built-in 512MB. So, if you add a 512MB DIMM, you'll have 1GB while a 1GB DIMM will give you 1.5GB. A 2GB DIMM will give you 2GB, not 2.5GB, because the last 512MB will be ignored. Still, it may be worthwhile to spend a few dollars on a 2GB DIMM, just so you can max out your RAM.