any good light shareware/freeware to detect hardware configuration?

[Jason Stephenson]

The previous two suggestions are pretty solid, and I'll second the 
Knoppix suggestion.

However, my usual approach to used hardware (and I deal with a lot of 
it) is to open the case and take the parts out. I generally write down 
the serial and part numbers and maker names off of the bits and pieces 
and then start Googling for the stuff that I've not seen before.

Cheers,
Jason