It depends. If you're happy to have everything put into the library folders defined by the vendor, then Renderosity downloads have a consistent format and you should be able to just unzip everything to the same place. I use 7zip in command-line mode when I want to unzip a load of stuff all at once. I'm assuming you use Windows here.

If you're fussy about your library structure then there is no substitute for manual rearrangement after unzipping. Many freebies have non-standard folder structures and will also need manual intervention.

At the risk of sounding smug, may I recommend a backup before the next drive crash? ;-)