Well, the optical drives can be reused.
The hard drive can be used as long as it works... just reformat it and use it for storage or something.
The RAM could be reused, but it is PC2100, which is very slow by today's standards. Better than nothing, but slower.
The power supply is 200W and is proprietary. Throw it as far as you can...
The mobo, fan, case, and anything else can be used as a doorstop...