"For the Lenovo S10 you need a DDR2 PC5300 SODIMM (this will not fit into a standard SDRAM SODIMM socket). A SODIMM, or small outline dual in-line memory module, is a smaller alternative to a DIMM, being roughly half the size of regular DIMMs. SODIMMS are often used in systems which have space restrictions such as notebooks and netbooks.Click the link above to get linkies to ram, batteries. Or just search Amazon. Sweet.
Lenovo's IdeaPad S10 netbook is easy to upgrade. The S10 has 512MB soldered onto the motherboard and only one SODIMM slot. If your S10 comes with more than 512MB preinstalled, than there's already a SODIMM in the slot and you will have to remove it first. The motherboard also cannot recognize more than 2GB in total, including the built-in 512 MB. A 2 GB DIMM will give you 2 GB, not 2.5 GB, because the last 512 MB will be ignored"
Now to decide 'tween Dell Mini 9 and Lenovo S10.