> Is it possible to store grabbed information using
> the W/ARC format when using HTTrack?
No, this isn't possible.

> Of maybe tools
> to convert grabbed data to this format?
Well, this is something I may code one day, yes. The current httrack format is
however not very hard to extract (this is a regular ZIP file)

> I've read that ProxyTrack will be able to handle
> W/ARC in the (near?) future. 

ProxyTrack has ARC format support scheduled, but it means that you'll be able
to use it with ARC files, NOT convert anything. However, this project is
currently not very active, mainly due to lack of interest from users.