Windows XP Tips 'n' Tricks
Please note that some of these tips require you to use a Registry Editor (regedit.exe), which could render your system unusable. Thus, none of these tips are supported in any way: Use them at your own risk. Also note that most of these tips will require you to be logged on with Administrative rights.

Unlocking WinXP's setupp.ini
WinXP's setupp.ini controls how the CD acts. IE is it an OEM version or retail? First, find your setupp.ini file in the i386 directory on your WinXP CD. Open it up, it'll look something like this:
ExtraData=707A667567736F696F697911AE7E05Pid=55034000
The Pid value is what we're interested in. What's there now looks like a standard default. There are special numbers that determine if it's a retail, oem, or volume license edition. First, we break down that number into two parts. The first five digits determines how the CD will behave, ie is it a retail cd that lets you clean install or upgrade, or an oem cd that only lets you perform a clean install? The last three digits determines what CD key it will accept. You are able to mix and match these values. For example you could make a WinXP cd that acted like a retail cd, yet accepted OEM keys.
Now, for the actual values. Remember the first and last values are interchangable, but usually you'd keep them as a pair:
Retail = 51882 335Volume License = 51883 270OEM = 82503 OEM
So if you wanted a retail CD that took retail keys, the last line of your setupp.ini file would read:
Pid=51882335
And if you wanted a retail CD that took OEM keys, you'd use:
Pid=51882OEM