The guitar in this wallpaper is either an electric guitar or an acoustic guitar. The guitar strings are steel strings so it's hard to tell what type of guitar this is exactly.
One thing I do like about this guitar wallpaper and the guitar that's shown here is that the guitar have a very nice looking inlay in the fretboard.
The fretboard and frets looks very clean also and this is a plus.
Now the size of this guitar wallpaper is only 500x375 so it's not a very big one. But because of the HD quality of the guitar wallpaper this will actually not look bad even if you stretch the wallpaper on you're desktop. And it will also look good for you that are using widescreen computer monitors.