DBVM is a virtual machine that will run your operating system and expands the instruction set to allow usermode application access to kernelmode. And it allows to let programs redirect the flow of system events to different locations and change their results. (For example redirecting a interrupt to a different interrupt handler without editing the interrupt table)
Cheat Engine can make use of these added instructions to make game modification and debugging easier. Especially in Vista 64. To make use of it, just boot up with DBVM, which will then boot up your operating system, usually windows, and Cheat Engine will automatically detect that DBVM is loaded and make use of the added functionality.
Safety: DBVM can be used by mallicious software. Therefore it requires a 64-bit long key to make use of the instructions. One of the instructions is to change the default key to a different key so other programs can not use it, without the proper key.
Please note, the current implementation of DBVM requires your cpu to support the intel-vt instruction set. For a AMD version please donate enough money so I can buy a AMD system to test the AMD specific code on.
One easy way to find out if your system supports dbvm is rigthclicking on the CE logo to show the about screen. It will tell you if your system is capable or not. And if you actually have dbvm loaded, it'll even tell you which revision of dbvm you are running