Re: newbie - porting to Java
I'll try and answer part of your question. If you have a .DLL written in VB6, then it will be a windows DLL (and presumably it'll be the same with the C++ DLL). Therefore, logic dictates that you probably can't run them on a linux computer. Whatever libraries you try and use will have to be written in Java.
As for the connection with an Access database, I assume it would work (guessing here, nothing certain). The list of JDBC drivers here mention "Microsoft Access" and the drivers shouldn't be OS specific.
Re: newbie - porting to Java
Well, I've never used Access DB on linux but I can tell you I've opened Access DB in OpenOffice on linux (which is supposed to be Java based) so I'm pretty sure you can. You just have to look up the connector. I think Microsoft MSDN would be a good place to look