Any upgrade or downgrade has a risk of problems, so it is important to backup the system in case the computer is left unbootable.
Also, anything else you wish to keep is safe.
Easeus Emergency disk should be created via the Tools option.
To re-install Vista, simply boot from the DVD and follow the instructions.
You may need the License key number from the label under the laptop (or in the battery compartment).
An alternative scenarion, is that you forget about Vista downgrade just now
Upgrade to W10 instead. You don't have to keep it if you don't like it, but it is Free for now and automatically registers your laptop as 'W10 Qualified'.
Your existing W7 embedded License is sufficient for the upgrade.
You can make a note of it with Advanced Tokens Manager, in case it might be useful at a later date.