The $140 version is likely an OEM copy of XP Pro, while the $200 version is a retail copy. Both are likely to come with SP2 integrated on the CD (if not you can integrate the service pack yourself prior to installing). OEM copies are for system builders/resellers and can only be sold when bundled with some piece of hardware. They are cheaper than their retail counterparts, but have limitations as well. You will not receive a manual nor will you be able to receive support from Microsoft directly. OEM copies are also tied to the original machines they are installed on. You will not be able to (legally) uninstall your copy of XP from one machine and install it on another (although there is no technical limitation preventing this). Retail copies include support and they are only tied to the license holder (you can uninstall your copy on one machine and install it on a different machine according to the license).
That said, many DIYers purchase OEM copies for the cost savings alone.