more RAM always helps, so if your not going to be charged for it, I'd say try it.
My experience is that Vaio's are very stable and reliable even if they can be slow.
What processor is it? If it's a celeron I've known them to overheat and cause significant slowdown.
If it's a second hand system, have you reformatted since you got it? Sometimes helps. Don't forget to back up though if you do that!