I am using Delphi 7 but I have trialed the Delphi 2005 - 2010 versions.
In all these new versions my CPU utilization is 50% (one core is 100%, the other is \"relaxed\")
It's the code insight or other IDE feature, compiling stuff in the background. It's pretty normal for D2005 to go into "zombie" mode for half a minute or so and swamp one of my cores. It seems to be much better in D2010 though. Try turning off the IDE gizmos (code completion, code parameters, tootip, error insight, etc..) and see if that calms things down. If it does, then turn them back on one at a time and see what you find.