Two products come to mind, though I can't say for sure they'll let you boot from an external hard drive. Norton Ghost and Acronis True Image are probably what you're looking for. They will make exact copies of your system at a specific point in time, and then allow you to restore your system back to that point.
There are probably other similar programs out there, so feel free to look around.
Now I have a Vista PC that is up to spec and in case it crashes; I want to have something to lean back on. If I could use my backup hard drive in this case would be perfect.
Is there a program out there that will copy everything and turn it into a boot file of an external hard drive so when I reset the computer it was just as it was when I backed it up, if so tell me.
Dell XPS 400
4.0 GB RAM
3.0 GHz processor Intel Pentium D
BIOS Revision A07
Windows Vista 32-bit upgraded PC