Take this with a grain of salt if you will:

WARNING: I've found many web sites recommending a way of speeding up boot times that may in fact slow down the amount of time it takes to boot up, and will probably slow down application launching as well. The tip recommends going to your C:\WINDOWS\Prefetch directory and emptying it every week. Windows uses this directory as a way of speeding up launching applications. It analyzes the files you use during startup and the applications you launch, and creates an index to where those files and applications are located on your hard disk. By using this index, XP can launch files and applications faster. So, by emptying the directory, you are most likely slowing down launching applications. In my tests, I've also found that after emptying the directory, it takes my PC a few seconds longer to get to my desktop after bootup.

This doesn't apply to hacking it in the registry of course, but in my experience, i just leave it alone.
One that 'has' helped a' bit however,is this one:

Enable Quicker Startups with a Boot Defragment
There's another way to speed up XP startup: make your system do a boot defragment, which will put all the boot files next to one another on your hard disk. When boot files are in close proximity to one another, your system will start faster.

On most systems, boot defragment should be enabled by default, but it may not be on yours, or it may have been changed inadvertently. To make sure that boot defragment is enabled on your system, run the Registry Editor [Hack #68 of Windows XP Hacks], and go to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Dfrg\BootOptimizeFunction
Edit the Enable string value to Y if it is not already set to Y. Exit the Registry and reboot. The next time you reboot, you'll do a boot defragment.

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