I am not sure if you could dry them out in an oven or in a dehydrator. I mean I'm sure you could but I have never tried it. I have always let mine air dry. I'm sure there are tons of info on the internet though.
Here is a link on Anne Marie's blog about infusing herbs.
http://www.soapqueen.com/bath-and-body- ... nfusion-2/As for infusing a Pine tree I am not sure. I have never done that. I would see if you can find info online about using that type of plant for infusions.
Crock pots do work great for infusing, just make sure you keep the crockpot on low to avoid burning the oil or herbs and only ever use dried out herbs for infusions. Fresh herbs have a lot of water in them and can cause your infusion to grow bacteria.
Here is a link to a few really good posts by Amanda from lovinsoap.com on infusing too.
http://www.lovinsoap.com/category/color ... ly-series/