Freebase Dali

To the OP:

Yea, direct guitar signals are mono. Set Acid to record in mono, and your signal should be straight up the middle. If you want to achieve stereo spread, you can simply record another track along to the original, in mono, then pan each track opposite of each other. That will sound better, or as good as recording directly from your guitar could ever sound. (unless you're planning on using an amp simulator, in which your guitar signal doesn't need to be stereo to begin with)
Simply using a stereo TRS connector and recording in stereo isn't going to be any different than recording in mono and duplicating the track and panning each track hard opposite. It will sound exactly like a single mono recording, as both signals are identical and will present themselves as directly centered in the stereo field. (Unless you alter one tracks volume, which is essentially the same thing as panning to a side) And you probably don't want to duplicate them anyway because of the possibility of frequency cancellation, which will result in a lowered output of your signal while not doing anything productive with it unless you're planning on filtering each track differently.

Of course, if you actually meant "I played my guitar through an amplifier plugged directly into my computer", then your output from your amp's headphone port, or line-level output, should be connected to your LINE-LEVEL input on your sound card, via a stereo cable with what I'm assuming will be a 1/8 inch TRS port if it's a built in sound card, and probably a 1/4 inch port on your amp.
In this scenario, you'll want to set Acid to record in stereo... mostly if there are any stereo effects employed in the amp, like delay or reverb.