If you've got free energy and the hardware is just collecting dust, go for it, although you should be aware that you won't be able to bring in much. Looking online, the 100 and the 120 are fairly old, in the sub-1GHz range for the SPARC processors. The pentium 4s won't bring in much either because they're CPU-based, but it's worth a shot.
The i7 + a 295 can bring in some money, but not a ton. You could throw and AMD GPU into it if you wanted to mine much faster.
Overall, if you throw enough hardware at this, you could bring in SOMETHING, but don't expect to make any meaningful income off of this. You'd probably be better of craigslisting the Pentium IVs.
well the powercost is free so i guess its worth a shot