All the links on http://technet.microsoft.com/en-us/virtualization/bb545897.aspx seem to be broken.
Don't use that, it doesn't work with Hyper-V (if you're still running Virtual Server you'd better be planning an upgrade, soon). The SysInternals Suite includes Disk2VHD, which can do the conversion, though you'll likely have to muck with the disk drivers or the virtualized system will not boot (you'll end up with a STOP 7B.
The general steps for using Disk2VHD:
If you're going to be doing this on multiple machines I'd recommend a fully automated tool. Microsoft provides this functionality in SCVMM, which you can download a free trial of too. There are other utilities out there, Acronis and others.
Full Disclosure: I work for an MS Partner