Assuming you have optical media, it's about a half-hour procedure max. Super clean, at least in my experience. I installed XP on a virtual box the other day and it was like waiting for a glacier to melt by comparison. Win7 is much faster than that.
If you do not have optical media and need to install from a USB thumb, let me know - there's a couple of wrinkles but when you get it worked out that sucker flies. That's the way I'll be installing from now on...
I may be doing that in the near future to a netbook. Why don't you just post your method?