A website has reported pre-release details about the last service pack for Windows XP.
The details were divided into six different sections. On the second section, it notes that those who are using the Windows XP Media Center Edition or the Windows XP Tablet Edition can only get the service pack via Windows Update.
This service pack will be an optional supplement for OEMs according to the fifth section. The author of the article notes on the third section that instead of 3 waves, the languges will now be released in just 2 waves since Microsoft will combine waves 2 and 3 into just 1 wave.
Source: Techarp

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Not sure how accurate that is, especially the second section. I d/l’d Sp3 via Technet and installed it on my home machine which runs XP MCE with no issues. It reports SP3 on My Computer.
Actually this info is not completely accurate. The article states that SP3 will be available for manual download on April 29 when, in fact, that is the date set to begin offering it as an Automatic Update.
As of April 25th, SP3 Build 5512 (the final release) has already been available for download to MSDN and TechNet subscribers and has already found its way to sites like majorgeeks.com.
It is also misleading in making you thing that the final release of SP3 is a 544MB+ download when, in fact, it is still only 316MB. The 500MB+ is the complete size of the install CD AFTER integration of the service pack or the approximate size of the retail CD…if they planned to offer one.