That's pretty realistic for an experienced builder. The most time-consuming part, in my experience, is patching Windows, and that takes a long time, even starting with Service Pack 2. My brother is a bit more tech-savvy than I am, so he created a slipstreamed version of his Windows install disc, so that he can re-install and need almost no patching.
But for the physical assembly? Hour and a half sounds reasonable.
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