The first thing you need to ask yourself is if you want to invest a good amount of money and time. What a lot of people see with bitcoin mining is a get rich quick scheme, which I can tell you it is not. You'll need to invest in good hardware if you want to have a decent to good hashrate (higherhashrate = more coins), and you'll need to wait many days (45+ days) for your hardware to get you some coins, even on mining pools. Also, being good with computer hardware (as in maintenance, overclocking, and building computers) comes in very handy. If you want to invest your time and money, start looking at the how to get started topics all around the newbie and mining threads.
A fair warning, old PC's don't really mine well. Processor mining is overshadowed many times by GPU (graphics card using opencl) speed. If you want to be able to mine well, you'll need to invest in good graphic cards, like the ATI 5XXX and 6XXX serires (not mobile ones found in laptops).
I don't want to sound to deterring, but most newcomers asking these questions don't usually know what they're in for.
hello. Im sorry if im of topic.. Im new in mining. Ive been looking at bitcoin for a while now. The difficulty to mine is high bacuse of the hash rate right? The problem is im running an old pc.. Therefore, i think i want to mine other coin such as monero because of the lower hash rate. Its a good idea?
Unless that old PC of yours have at least 2 XEON processors or a good graphic card it cannot mine Monero to see any profit and even with those processors you can make only 8 Usd a month (personal testing with 2 XEON 5650 old processors).
However you can put your processor to good use if you have a good one, anything quad core will do. You can download Minergate and mine BCN(Bytecoin). This should give you about 3000 BCN in a month or 0.0021 btc in a month.
As you can see the amount is ridiculous so CPU mining is dead from long time.