JenBurdoo, dulcimers and guitars are similar in that they both have strings and can be strummed or finger picked. However, the number of strings and fret patterns are different and lend themselves to different techiques.

While guitar is a chromatic instrument, i.e. all of the notes in the scale are represented by the frets, dulcimers are diatonic and have to be retuned (or use a capo) to play in different keys.

Additionally, due to the diatonic fretting and there being only three strings (sometimes four, but the melody strings are a double course and tuned to the same note), chording can be problematic as often you're not getting a full chord, but only two of the three notes. Because of this, dulcimers tend to be melody instruments rather than chordal (like the guitar).

None of this is meant to discourage you from picking up the dulcimer, though. They're great fun to play and once you know what you're doing, very versatile.