If you are using 50% of one CPU for the game, you have a problem. If you are using 50% of the combined power of both CPUs, that (I think) is expected.
You may however have some background tasks on the same CPU as the game.
I just re read the quote. Is the P4 2.4 HT xtreme a single CPU?
Yeah the P4 is a single processor although dxdiag shows 2 and task manager shows 2 cpu panes. Still only 50% in tower...jumps to maybe 75% in heavy action. The video card is only an Nvidia 7300GT 512MB vram...only uses 92max and I'm getting 60 to 72 frames...I might have to update the driver on it.
The dual core system is showing 50% on both processors with the game running as well...better video card...better performance.