When you open the system monitor it does eat up CPU for a split second. I have a computer with X64 loaded on it. I noticed for editting this is the way to go. I am finding that I am having a hard time getting drivers for certain things though. When I use the 64 bit PC to edit on, I see 1/2 the cpu usage as when using 32 bit. I basically gives you 2 times the width as 32. Every time you open a new plug in and run it it will draw more bandwidth. I have a software called CPU burn in. It is supposed to run your CPU at 100% for burning it in. I ran it on the PC with 32 bit windows xp with 2 GB of RAM. It ran @ 100% like it was supposed to do. Then I formatted and installed windows XP Pro X64 and ran it and it only ran it at 50%. The only thing I did was take out 1 GB of memory after re installing X64! 1/2 the memory and still only used 1/2 the bandwidth! I used the extra memory in my recording PC. There are ways to make windows not use as much CPU you can go to this link and see some ways. I have used trial and error on this.
Maximize the Performance of Windows XP, from O'Reilly Media - Downloads - TechRepublic