Due to the GMA 500 on the VAIO P series Linux is not a good choice. It's not impossible, but the video drivers will be a pain. The proprietary driver has not been updated for recent kernels and the open source ones only have very basic 2D acceleration and no 3D or video decoding. If you go that route then a lighter weight distro like XUbuntu, LUbuntu or similar would do well.
Thanks for your advice, washu.
Actually I've given a try to several live distro, more or less they all have some weird issues (with graphics, but more often with audio, and awakening from sleep too): broadly speaking, the newer the version, the more likely you're running into problems with the Vaio P, right out of the box (I don't know whether installing an older but rolling release may be better: what do you think about?): up to now the "best" (less issues to address) candidates are LuninuxOS 12, Elive Topaz, and openSUSE 12.2 (I was not able to force 13.1 to recognize Intel HDAudio), even if I loose the ability to run decently flash videos, even with the "infamous" Google Chrome; still broadly speaking, usually Xfce desktops gave me the worst experience (OOBE), and I'm not talking about "eye-candys".
Your best bet is Windows 7. It should run reasonably well with the SSD, especially if you have a model with 2 GB of RAM. There is an official Win 7 32 bit driver for the GMA 500 which will let you use it to it's fullest. I've run 7 on several older Atoms and while it is not fast, it's quite usable.
I will give a try to W7*32, even if Vista*32 was just awful then.