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>Nonetheless, to get it to work he'd probably need a static IP (usually an uptick in cost from basic ISP service),

I don't believe this is true using VPN. It is either VPN with computer name, or a static-IP. My source (which does not make the point clear):
http://www.microsoft.com/windowsxp/using/mobility/getstarted/remoteintro.mspx

>All of the above problems are avoided/bypassed by proxy services such as GoToMyPC. If you can handle the monthly or yearly cost it's a pretty compelling solution for casual and/or non-technical users, and worth consideration even for advanced users.

I agree completely. We have a (small) corporate gotomypc account here, and I can easily set different people up when they travel, or whatever, and it doesn't matter what flavor of Windows they have on either end.