When I got my last PC (nearly 2 years ago) I had XP on the new one, and Windows ME on the old. I had GB's of data I wanted to transfer and couldn't be bothered swapping HD's accross. Instead I used this little thing...
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I copied all files I needed to one dir on the old machine, setup the link between the two machines (took a bit of configuring, but got it working in the end) and left them to copy. I woke up the next morning and everything was accross. They're cheap and handy. I think PC World have the same thing, but at a multiple of the cost from eBay. I orderedd mine from a place in Hong Kong and it arrived within a week.
Hope that helps....