The tricky and time-consuming part is going to be downgrading that PC to windows XP (specifically getting all the hardware drivers working properly). You might be paying someone the 100.00 for that alone, and another day's session for all the other stuff.
Agreed. There's a good 2 hours 'dead time' watching XP and all its updates install. Ideally you'd be in a position to let the person doing the work take the PC away for a day or two. That way they can monitor the install progress and make the occasional keypress/mouse click while essentially getting on with other things.