The answer is no way. At least, the standalone version of IE6 under my Vista is consistently giving an error, and I haven’t found any working ways to launch it.
But it
turns out that there is a way out of this problem.
All you need is to force IE7 to behave like IE6, and thanks for this output you need to tell Microsoft.
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First of all, you need to go
here and download the User Agent String Utility version 2 from Microsoft.
This wonderful program at startup shows the following window:

Accordingly, if you select the right checkbox, Internet Explorer 7 will emulate IE6, and you can check your layout on it.
There is only one problem: to download this program, you need to be the owner of the licensed version of Windows Vista.
upd: As confirmed in the comments, this does not turn IE7 into IE6. This only replaces his user agent.