Actually, win32dd is the only 100% open-source tool to capture memory under Win2k3 or Vista. Even, if ManTech released a similar tool yesterday, but some part of the source code (e.g. driver source code) are missing. Then, I decide to release mine as a full open-source project under GPL3 license.
The main difference between ManTech tool and win32dd, is that win32dd is mainly a kernel mode application — then it avoids to use user-land API to write to an output file, everything is done with native functions. Thus, it means a faster dumping… This point isn’t negligible when you have one million page to dump in one single.
In ManTech tool, the driver is only used to get \Device\PhysicalMemory handle.
EDIT: (16th June), New version, fixed bug.
PS: You can read further information about PhysicalMemory restriction access on the Microsoft MSDN here.