It's 7.5.3 (the one freely-distributed on Apple's site). Guess I should have been more specific. :I

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Do all the installers, eg 7.6, 8.0, 8.5 report the same thing, or is it only the 7.5.3 installer?

Could you not live with 7.6.1?

What do you mean by "zeroed the drive", have you run Drive Setup (or whatever) created one HFS partition and formatted it?