What is Nashville guitar tuning?
Nashville Tuning uses exactly the same notes as standard guitar tuning, but in different octaves. It uses only high sounding notes and contains no bass strings. The result is a unique bright treble sound that is fantastic when played alongside another guitar with regular tuning - especially useful for recording a 12-string guitar sound when no 12-string is available. Nashville Tuning is played is played using the same chord fingering as standard guitar tuning, but the resulting sound is different because it is using the same notes in different registers.
Tuning your guitar to Nashville Tuning
The reason that Nashville Tuning sounds like a 12-string guitar is that it uses the same notes and the same strings. The individual string notes for Nashville Tuning are as follows:
1 - E (as per normal tuning)
2 - B (as per normal tuning)
3 - G (one octave higher than normal tuning)
4 - D (one octave higher than normal tuning)
5 - A (one octave higher than normal tuning)
6 - E (one octave higher than normal tuning)
To acheive this tuning you need a specially-selected set of string gauges - don't try it with a regular set of strings! This is exactly the same tuning as is used for the extra course of strings on a 12-string guitar. If you took off the regular strings from a 12-string, you'd be left with a Nashville Tuned guitar.
So if you want to try Nashville Tuning you need to either buy individual strings of suitable gauges, buy a set of 12-string strings and use half the set for your Nashville Tuned guitar or buy a set of special Nashville Tuning guitar strings. If you use a 12-string set for Nashville the other six strings won't be wasted, as they will be the same as a regular six-string set. The easiest way to try Nashville Tuning is to but a dedicated set of strings. These are easy to buy online if your local guitar store doesn't keep them in stock.
More on Nashville Tuning here: http://guitarstringguide.com/drupal/nashville-tuning