I have had trouble optimizing a H-P aka Compaq Celeron (512 mb 3.46 ghz) machine that is running Windows Home XP Home Edition. My experience could save someone countless hours of frustration - been there, done that.
Problem reared its head when I tried to "Set Computer to Standard PC NOT ACPI PC" as outlined in the Optimization Guide. After following the the outline to the letter (more times than you want to know), my computer would not reboot. It took me many unsuccessful attempts before I realized that this change was causing my problem. Each time I had to reboot and restore my computer in order to get it to run. Last time out I followed the optimization guide with the exception of this section and did not have any more problems when booting up.
You may want to consider this before attempting to change your system
Bob @ BobsShop