I believe "sheetrock" is what we in the UK call "plasterboard", right? A half-inch thick sheet of plaster/cement/whatever with paper covering either side?

I've used plasterboard fixings to hang my fiddle and mandolin on a partition wall. I don't think I'd trust them for anything heavier though. My guitars are attached to exterior walls where a rawlplug can be use. All these use StringSwing hangers which are fairly nice to look at (varnished wooden backing plate, metal prongs to hang instrument on).

I'm also lucky in having a wife who'll let me display them in the living room, since we both think they're at least as attractive as paintings. :-)

Graham.