In the IT world, there are a number of amusing jargon terms for commonly-performed routines. In this case, the 'salute' is (likely; I have no canonical reference for this, as the Jargon File merely calls it a synonym for the Vulcan Nerve Pinch) intended ironically as a mark of (dis)respect towards Mr. Gates' most well-known products.
The earliest reference I've been able to locate comes from an FAQ from 1994, where the familiarity with the term indicates that it's been in common use for some time. I suspect that if I had access to usenet archives that the initial usage would be found sometime earlier, probably in the comp.sci newsgroups.
This bit of jargon has held up rather well, as it's still very much in common use today amongst IT professionals; the usage as an authentication prerequisite in windows-environment systems (which I've thought to be a spectacular joke, personally) has only rendered the use of the term more common.