My MacBook freezes there a way to bring it out of frozen?  What would be causing it to freeze?

My MacBook freezes @ least once a week.  I have to shut it down.  What might be causing it to freeze & is there another way to bring it out of frozen other than shutting it down?

Not enough free space on the disk can cause the system to freeze...
Right or control click the MacintoshHD icon. Click Get Info. In the Get Info window you will see Capacity and Available. Make sure there's a minimum of 15% free disk space
Check the startup disk in case it needs repairing >  Using Disk Utility to verify or repair disks
MacBook, Mac OS X (10.6.5)  <  your profile
If that is correct, when you can, you need to update to v10.6.8
Updates are available from your Apple menu > Software Update...
Not enough RAM can cause the operating system to freeze also. You may want to consider increasing memory. To see how much memory you have installed click your Apple menu icon then click About This Mac. That will prompt the System Profiler. See Memory under Hardware on the left.