Well, like I said, If I had a choice, I'd go with the wired approach, but with my dad, it's one of those "my way or the highway" sorta things.
Oh, and Aaron: If you do plan to integrate the other two, it would be wise to switch all the computers to using "infrastructure" mode first. It'll probably be easier for the two new ones to get settled in.
And, lastly, my dad is running a mixed network. He's got his PII 266mhz and my sister's P1 233mhz (yep, that's my old system!) on a physical wire, but both my 1.5Ghz and dad's new laptop are using wireless.
So far, everything's working without a hitch, the laptop is using WinXP, all the others are using Win98SE.