Beagle is set to index files when the computer is idle. Have a look in Menu → More Applications → System → Search Settings → Searching: and change the settings from automatic. Just to see if the load on the CPU drops off.
If you set Beagle to run when the computer is idle, you should see after it catches up, that it rests and doesn’t appear to intrude on your resources.
I used to uninstall Beagle in the early days because it was resource hungry. Now it seems to behave as the developers wanted and only come in after I’ve finished (computer=idle) and then shut off when it’s indexed the few extra pages I generated.