The first block took 5~6 days to mine, yet there's no tell if it was a constant work and the total hashes produced is also unknown. So any exercise on such grounds leads nowhere.

Assuming it was a continuous work, then his computer was way worse than a 1.3 Ghz Sempron, probably Pentium II or III (which were way old by then).

As for Vista, someone with more resources would be able to get the software tested with it. Bitcoin project took him some time wasn't like he was in a rush to release it.