By two ways u may configure the priority of course from command Line,
Goto Command Line and type sc, It display and configure background rocesses (services). and or type schtasks, that helps to schedule commands and programs to run by the server 2008.
U can also use taskkill to stop a running process. OR from GUI thru Task manager u also configure the same.
OR u may download “Process Priority Observer” a tool that helps to configure/observe the running process.