I'm wondering if you've considered fiberoptics for your garden? The nice
thing is that there is little worry about weather damaging the source and
the new tips for FO are extremely versitile and give off attractive light...
very low energy cost, big-time control over effect and placement...

http://www.luciferlighting.com/fiberoptics.htm gives you an idea of some of
the stuff that's available...
http://www.advancedlighting.com has some good product info... just to get
you started.
google search turns up a vast number of good sites to check out as well...