Supported memory configuartions: http://www.kb.sony.com/selfservice/m...=0 0 138864652
An option with one 1GB stick and one 512MB is included.
I worry about mixing different makes of RAM. It should work, but I've had it fail. As you can buy two 1GB DDR2 SODIMMs for $36 (+ shipping) from www.newegg.com
(if you're in the US or Canada), I suggest that you go for the full 2GB, and save yourself some potential headaches.