OEM Windows OS licenses are usually tied to hardware. Dell's OEM installation of XP will have come with a reinstall disk that should only work with Dell hardware.
The unique platform license is generated from an install medium key and hardware data such as processor and hard disk serial number. That's why if you've ever had to replace a major part of a Windows machine (HD for example) you need to re-authenticate the Operating System. Nowadays that can be done online or by phone to MS.
The reason for a machine-unique key is of course to stop users installing Windows on lots of machines without paying for licensing.
As it seems you will be running Linux you shouldn't need to worry about Windows licensing. Can you boot the Dell into BIOS setup mode and disable/delete disk ID there? (Tap the F2 key as soon as the Dell logo appears).
- Or Google* "replace dell laptop hdd with ssd"
*Other search engines are available.