[1llusion]

I only have one PC to spare. I guess I will join one, trying to find one with the lowest fee. Does it matter which miner I use or are they all the same?

Bitcoin Mining can be quite CPU intensive, hence Depaus's recommendation for multiple computers as most of the professionals actual use.

If you aim to mine for real. It is suggested to mine through your graphics card.

I used to use Guiminer and found out one thing, if you have more than one graphic card, launch the miner once for each of your cards for maximum performance. Also, Slush's pool is kinda nice from my experience (and I'm not saying it just because the pool owner is Czech )