Dave wrote:

I'd like to try taking photographs of such things as drops of water, or
exploding balloons.

What would you use to capture this with a digital SLR (in my case, a
Pentax K100)?

Here's a good site to get you started,lots of make your own stuff if
your handy,lots of advice anyway.
http://www.hiviz.com/

Thanks. It looks like I need to set the camera for a long exposure, and
then use something to trigger a flash unit.

So I guess I need, as well as a trigger kit, a flash unit which can be
triggered by a signal from a trigger.

What kind of flash unit would be suggested? I have an old flash unit
from my Praktica, but it doesn't have an input for a trigger.

Daniele