[HANASHIR:9109] halacha against instrumentation

[H & R Shubert <notfranz...>]

I'd like to pose a question regarding the origin of the halacha against 
instrumentation on Shabbat.  Having been raised in Reform Judaism, I may not be 
fully aware of the halachic implications of playing music on the day of rest.  
I have always assumed it is because the playing of instruments is regarded as 
"work", while devotional singing is not, much as driving to shul is forbidden, 
but walking is accepted.  Have I missed something?  Is there a more specific 
law against the use of instrumental accompaniment?  If so, can someone direct 
me to the source?

Thanks,
Rachelle Shubert