Windows Vista's first service pack, which has yet to be officially released, is widely available online. A quick search on bittorent tracker, Thepiratebay.org, shows that SP1 (Microsoft.Windows.Vista.SP1.Update.32Bit.RTM.Build.6001.18000.Re) is being distributed by nearly 700 seeders.
The release to manufacturing (RTM) is the last step before the code is officially released to the public and has been shipped to computer manufacturers and developers on the 4th of February.
Mike Nash, from Windows Product Management group at Microsoft, has provided with a useful timeline for SP1 availability for current Vista users; starting from Mid march, SP1 will be provided for end users to download at Windows Upload, with a full automatic roll out expected in mid April.
A few Vista users won't be able to download Vista SP1 if some device drivers that were identified as being problematic are found on the user's computer.
According to data posted by the group, nDN, who released the code, the 434MB RTM service pack file is a stand alone update that can be installed on any version of Vista RTM but not on the full OS ISO.
French website PC Impact, on the other hand, reports that Windows XP SP3 is on target to be released on the 23rd of March 2008.