Would acoustic guitar be hard to learn if I already know how to play the violin well?

The fact that you have calluses on your left fingertips is your primary advantage. You probably know music theory and that, too, is a great advantage that many beginning guitarists don’t have.

Rhythm and chords are all important for guitar playing and I’m sure you can make the transition from bow action, pisacato (?), and tremolo to chords and their progressions.

Buy a beginner’s guitar manual, such as Hal Leonard’s Beginning Guitar Method #1. Inside are instructions on how to tune, form chords, and play basic notated exercises for the guitar. I have every confidence that you will be able to excel at it.

Do it!

It’s great to allready have the musicial knowledge that you have….but the violin finger board is way smaller then the guitar, and the strings on the violin don’t hurt as much as the strings on the guitar, playing barre chords may be a problem at first as your not use to that at all…and barre chords can be quite difficult in the beginning it calls for a lot of strenght especially in your index finger….I teach acoustic and classical…and I tell all my students to first start on an acoustic when learning, so I’m glad that your going to do that. I would love to see you have a private teacher but if that’s not possiable it is possiable to teach yourself, it’s just that it’s easier with a teach….there are a lot of good sites that teach with a tutor, Cd, video, and DVD’s…..you can have your pick….of course you have to pay for their products….but there not much, at least I don’t think so. Some of the sites give a few free lessons to start…..maybe that will give you an idea if this is the way that you want to go. I don’t like the sites that give all free lessons as they are not complete….and I think that they leave the student hanging….I’ll give you a few at the end and you be the judge !!!!!!!!
http://www.meineke.free.fr/ (only good free site)
http://www.jamplay.com/ (6 free lessons)
http://www.billbrutal.com/
http://www.guitarchordsmagic.com/
http://www.justinguitar.com/
http://www.learntoplayguitar.net/
http://www.guitartutoronline.com/
http://www.absolutelyunderstandguitar.com/
http://www.top100guitarsites.com/
http://www.guitarforbeginners.com/
http://www.learn-to-play-guitar-online.info
http://www.guitar.about.com/
Free Sites :
http://www.guitar.about.com/
http://www.freebasicguitar.com/
http://www.abclearnguitar.com/
http://www.wiki.com/ (this site claims to teach you acoustic guitar rapidly, I’m not sure about that, so check it out and see what you think, I haven’t had the time to look at it lately)
http://www.8notes.com/ (this site has a lot of interesting things for guitarist, it even has a free electronic tuner on it’s homepage, and where it says chords, you can click on the chord that you want to lean to make and it shows you how to make it !!!!!!!!!)
http://www.cyberfret.com/
http://www.ultimateguitar.com/
The last two are tab for guitar, I don’t like tab, but I’m not sure if you going to read music notation, so I thought that I’d send a few, I hope that something here helps, and I wish you good luck, violin was my second instrument….I still say that someday I will get one and study it, bye !!!!!!!!!!!

You have the fingering and the bow. On guitar, you have the fingering but a guitar pick. You shouldn’t have any problem whatsoever. i agree that you have to position your hand differently.
At lease, you have an idea of the scales. I am a self-taught teacher and studio session guitarist. I am proficient at it. I mastered, reading, composing, chording, and allscales in all position.
My forte is my sense of instant improvisation and my good ear.