Is there a system freeze problem in Snow Leopard when there's no free memory?
The answer is simple: Safari just needs (or wastes) a lot of memory! If you only have 2GB RAM, use Googles Chrome Browser or Firefox. 

2GB of RAM is just not enough for todays Computer. Be sure to only open one app at the time, and close it when you are finish. 


  An Operating System handles the RAM by itself. When it's out of RAM,
  it stores the user-cache-data on the Hard Drive, so the Computer gets
  very slow.


And for browsing: Websites with lots of flash content needs more memory, than simple text sites. I've had a MacBook Air with only 2GB of RAM, and it was just impossible to work with!