What are the minimum hardware requirements for mining in a bitcoin pool? Note that I'm not looking for profitability, this has been answered numerous times. I'm more into setting up an old computer to learn how things work. But I guess there are minimum hardware requirements to be able to mine at all, e.g. being able to transfer blocks when a hash is found and a new block gets the attention. Are there any limits in the pools? Pools might not want participants that are so weak that they just create administration? If so, what is the minimum hash rate level, or is there another figure limiting pool access?
If you are purely out to learn, consider mining on the bitcoin testnet (the alternate bitcoin network that is identical except for running on a different port and allowing non-standard transactions). There you can even easily mine without needing any pool.
If you do insist on working on the Bitcoin port, really just about any pool should still allow you to participate. The question might be, though, what mining software is appropriate. If your choice involves downloading the blockchain, then its sheer size (>7 GB) may constitute a hardware constraint. But if you mine in a pool anyways, there is no reason for your miner to need access to the blockchain, unless you want it to verify that you do not unwittingly participate in a 50% attack.