Microsoft released another version of Windows XP Service Pack 3 on Tuesday, but the software remains in the test phase.

Unlike Windows Vista Service Pack 1, which was finalised in February and made available broadly last week, Microsoft has yet to give the final go-ahead for XP SP3.

"Windows XP SP3 RC2 Refresh was made publicly available today via Microsoft Download Center," Microsoft said. "We've made this release candidate available in order to receive further user feedback prior to the release of Windows XP SP3."

ZDNet blogger Mary Jo Foley said that she had heard that Microsoft planned to release it this week in final form, but since reversed the decision.

There's not too much different in the "refresh" from the RC2 version released last month, according to a TechNet posting. "Beyond fixes for common Windows Update issues, and the inclusion of support for HD Audio, there are no substantial differences between this beta release (build 5508) and XP SP3 RC2 (build 3311)," Microsoft stated.

For its part, Microsoft said the final release is still slated for some time in the first half of the year, with the standard caveat that its timing will depend on customer feedback.

Meanwhile, computer makers are supposed to stop selling machines with XP come June, although this deadline is likely to be extended.