Ok,, for a really nice explosion,, Hypervoxels are the way to go... Although mark might say with an animated texture and displacement.. You might get it with a sphere.... Hmm this reminds me of a maya dvd on custom shaders... Hehe.. :p Ok if you have by any chance seen the HDRI magazine.. a nice tutorial on realistic explosion was featured with Hypervoxels.. only thing to remember is the higher your settings the more render time you are looking at... Ok for a min long explosion... each frame i rendered was about 1 to 3 hours... Hehe yea,,, so consider a lot when you are rendering... Hmm you might be better off post processing to get the final look.
Hmm,, there is a plugin that will break apart and explode your mesh... Ok,,, you can do a search on flay.com on that... I cant really remember now... Something like C4... or something.
Ok my final thought would be now in Lightwave 8 there is hard body dynamics... So you might want to explore on that.
Ok i know i am not very helpful,,, but i believe in self exploration then guidence. So explore away. Remember before any large project you attempt remember to research.
There is always loads of techniques and ways around the problem.
Post your attempts and more help will come your way, i am sure.
Kumar