Can I migrate my existing physical WinXP environment (on a single c: drive) to a VHD via Disk2VHD and then run it on my new Windows 7 laptop as a virtual machine?
Microsoft's Disk2VHD is what you are looking for
convert your physical machine to a virtual machine
I've done the same thing but with VMware's converter and VMware Player / Workstation. Worked great.
The only real gotcha, that I'm aware of, is your XP license. If it is OEM, you're probably hosed -- or will at least have to call Microsoft to plead for activation. Converting to a VM triggers enough hardware changes that you (almost always) have to reactivate your license.