Really slow PC boot-up

Lately, it is taking forever for my PC to boot-up.  On the Windows XP loading screen, it takes about a minute and a half.  From the time my desktop appears until it is fully up and ready to use, another minute or two has passed.  I've cleaned up my hard drive and defragged it and I've eliminated the junk from my start-up.  I've run Ad-Aware to clear out any spyware.  I've cleaned the registry.    One of my next steps will be to using some sort of start-up manager to see what is loading and when and which things might be resource hogs.  But it seems to me that the problem is occuring before I even get to the start menu, as if the hard drive itself has slowed down dramatically.

Can anyone recommend any good hardware benchmarking/diagnostic software that I could test my HDD, CPU, memory, etc. to see that they are running at the speed they ought to be running at?