Question: So I gonna make a USB bootable drive of Hexxeh's ChromiumOS Flow. I want this to be able to boot into it on my school computer. The computers use Novel network and each student gets their own login. 

Can I use my USB drive to boot into ChromiumOS from the schools computer? I don't need to access the files on my Novel Login. 

So can I even do this?

Answer: 
You need to have single stick or matched pairs of memory. Which you need will depend on the system and some systems can take either.

If the system can take either it doesn't really matter whether you buy two 1GB or one 2GB stick - assuming that the specs are roughly the same.

Putting the 512MB in with a 2GB stick probably won't work.

However, double check your system specs on the Toshiba site to verify which you need to buy.
DDR2 modules must be used in matched pairs in modern systems.