TuneXP is a good recommendation for advanced users, but anyone downloading it might want to consider the following:
It's not listed here on NoNags. It's also not listed on my other favorite freeware sites (choices #2 or #3). Looking at it, I'm guessing the staff here would probably rate it 5 out of 6 "duckies". On CNET/Download.com, it's rated 4/5 by the editors.
Do NOT use this for anything beyond Windows XP (i.e. Vista or Win 7).
It's a technical app that would be listed on NoNag's Power Tools page. You should know what you're doing before you choose certain options, because some can't be undone easily. If you're going to experiment (play) with it, you should make sure your System Restore backup is current.
Put out by DriverHeaven (now HardwareHeaven.com) in 2004, but is no longer being developed. The links below are safe locations to download the Last Freeware version.
This radical, new tool is one of the best and most powerful Windows XP tweakers ever, having a few tweaks, which are unique to the program. Among them are: ultrafast boot (rearrange boot files); boot folder defragmentation; prefetch folder cleaning; DNS cache optimization; and file allocation size tweak. However, that isn't all. It includes a plethora of other performance tweaks, which will make your Windows installation run faster than ever before, as well as Windows Service configuration. For the first time ever, it allows the user to control a few of the most common performance suckers and annoyances.
CNET editors' review:
Although it might be a bit too technical for average folks, this tiny, free utility nonetheless offers a helpful set of optimization tools for more advanced users of Windows XP. TuneXP's interface is certainly no beauty, but since all of its tools are accessible via menu items, it's simple enough to operate. The Memory and File System section lets you perform tweaks such as accelerating DLL unloading and defraging boot files. The other system tools are organized into categories such as Internet, Hardware, and Services. While many of the program's features will go over the heads of those who aren't technically inclined, we're glad the help files fully explain what each part of the program does.