Ed,
All you need are some speakers (pre-amp, ie internal amplifier) with volume control.
Don't bother with anything with a sub, just another thing to bring around.
(So looking for 2.0 speaker, not 2.1, which is two speaker and a sub.)
Some like this will do grand.:
http://www.amazon.co.uk/GP-4600-Blac...575547&sr=1-10
I assume it only for the indoor hall.
Also if an old laptop, you might be better connecting via normal 3.5mm audio connector and not USB>
MiCk B. :-)