Amazon.com has published to its site Vista SP1 availability dates of Wednesday March 19. (Thanks to Computerworld for spotting Amazon’s SP1 availability notice.)

Microsoft officials have been saying for the past few weeks to expect Microsoft to release Vista SP1 through retail channels and via Windows Update in mid-March. Even though Microsoft released Vista SP1 to manufacturing in early February — and (after user protest) delivered the final SP1 bits to its TechNet and Microsoft Developer Network (MSDN) subscribers a couple of weeks after that — company officials said they were holding back on making the service pack more broadly available due to driver-installation problems.

(In late February, Microsoft inadvertently made a build of Vista SP1 available via Windows Update, and pulled it shortly afterward.)

Meanwhile, Microsoft has removed XP SP3 from its private Connect test site, according to testers who requested anonymity, in preparation for the delivery of the final XP SP3 bits.

Over the weekend of March 15, another new test build of XP SP3 leaked out. The latest XP SP3 build, No. 5503, was available on torrent sites over the weekend, testers said.

Said one tester: “A new build of SP3 is floating on the net, build 5503. The last build, the public RC2 was Build 3311 (which Microsoft released in mid-February) so it’s quite a jump between the two.”

The aforementioned tester said that the XP SP3 5503 build didn’t seem to include any noticeable new features or functionality. Other testers wondered whether the new SP3 build was real or fake.

Microsoft officials have said to expect XP SP3 to ship by mid-2008. Web site PCInpact earlier this year said Microsoft planned to ship the final version of XP SP3 the week of March 23, a date Microsoft would neither confirm nor deny when I asked.

Anyone else have more to share on XP SP3 availability?