Many acoustic instruments use a piezo contact pickup to provide a direct out for recording. The problem is most of the time the resultant recording sounds like it was recorded using a piezo pickup. One solution is to use impulse response files.
+++ HERE +++ is a forum post demonstrating a technique that can be used to change the guitar sound.
That is a very impressive demo!
My latest upload on the showcase features an acoustic plugged in direct (piezo pickup), I'm not setup to record with mics here.
To get it sounding half decent I used a similar set of EQ curves that were in the article Mario pointed to, and also added some additional reverb/delay. It sounds fairly decent IMHO but not as good as the one using the IR's.
In the demo they are loading the IR's (which are very reasonably priced) via TH3, but when I look at that it is quite expensive (almost $400) Are there other options?
EDIT: Never mind, just didn't look far enough, I see they have their own impulse loader, only $20. I'm going to download the demo and play with it a bit.