sql 2005 Express stalling / running very slow

Sql 2005 Express with XPP SP2 and the latest MS updates sometimes runs very slow.

A SELECT which should take a fraction of a second can take several 10s of seconds.

I have checked autoclose is OFF for database using

use master
go
exec sp_dboption 'your_db_name','autoclose'

And it is definitely showing as OFF

I've looked at the Activity Monitor and when stalled it shows one or two processes for my database which are sleeping with 1 or 2 open transactions. When I look at their details they are simple select statements.

Often when my computer should be idle SqlServer.exe can be consuming 20 - 30% of cpu

I've noticed that I have TWO sqlservr.exe showing in my Task Manager, Processes display

One sqlservr.exe is 27K using about 17% even tho computer is idle has username NETWORK SERVICE

Other sqlservr.exe is 343K using 0% has user name SYSTEM

I don't know why.

Wayne