I'm telling you I still think this is a bad idea. Doing a quick google search for "grapevine wood in aquariums" yielded me multiple results; all of them said to avoid it.
Here are just two links that document the problem.
I'm not saying it can't be done, because I too have heard of hobbyists using grapevine. I just wouldn't do it myself. Lots of potential problems, very little payoff. I'd suggest you hunt for other types of wood besides grapevine to use in your aquarium.
http://www.aquariacentral.com/forums...p/t-99665.html
http://www.fishforums.com/forum/gene...grapevine.html
http://www.plantedtank.net/forums/ge...driftwood.html