Does it copy files? Because, in my virus chest, i tried to extract 4 files, but it says it already exists, and it gives me an option to overwrite. The only way those files are already there is probably because i used vdrb once. Suggestions? 
You’re messing VRDB and Chest.
VRDB stores the necessary info to restore executables (*.exe, *.com) files.
VRDB is not a backup system, the stored information is very small (not the whole files).
Besides, only Win32 executables are processed.
The VRDB data are stored in \Data\Integ\avast.int
So it’s not a bakcup utility, but a restore feature of avast. VRDB is a generic method, storing file parts that are often target of virus infections. So, it is capable of fixing even some brand new virus infections.
Chest is Quarantine. The files “in Chest” are actually stored in a crypted form inside of the avast! installation directory. Leave them in the chest (they can’t do any harm there) for a week or two so as to ensure that there are no harmful effects from them having been moved there (incorrect detection, etc.). This gives you time to investigate if at all possible (google search, ask here, etc.) to confirm.
During the installation, avast! copies some critical system files into the Chest, under the “System files” category. Those files might cause the operating system to crash if they get infected by a virus. If needed, those files can be restored from the Chest to their original location. Should an unknown virus infect the computer despite the extensive protection from the avast! antivirus package and alter an important system file, it can then be easily restored to its original state.
There are (generally) files in the System Folder of the Chest: command.com kernel 32.dll and wsoch32.dll
Besides what Tech said the VRDB and the Chest are unrelated. What are the files you are trying to extract from the chest (and what was their original location) ?
And possibly more importantly why ?
I have been using Avast! home for over a year now and have never created a VDRB. Am I compromising Avast’s ability to repair a file? I am a little confused about the VDRB myself.
Sure. That’s VRDB purpose… avast uses VRDB to repair executable files the get infected.
Whilst there only certain things that can be repaired (trojans can’t as the file is completely malicious) you are slightly compromising avast’s ability to repair those files it can repair if infected.
Check the avast help file, healing, VRDB, see image (click to expand).