I have SBS 2008 server with 16Gb of ram that I am having issues with lock ups. It usually locks up when changing USB backup hard drives. I have noticed that the sbs SQl instance and their SQL instance are taking up large amounts of RAM. I have tried limiting the amount of memory that SQL uses through command line but after I reboot the server it seems to go back to the way it was. I have done all the recent MS updates too.