I've read that on the +5 line it sends in output 30A or 2A, this can damage the circuits?
Power supplies don't "send" their current, the consuming device "draws" what it needs*. So a device using say 1A will not be overwhelmed by a say 30A supply; but you would be able to run 30 of them!
Have a look at Instructables for some instructions on hacking an ATX PSU.... this
is a good one.
I'm converting one this very week... haven't done the fancy work yet- terminal posts etc- but have tested it. I currently have 3 servos running from 5v, and I hacked a USB-B cable which I've wired in to 5v too and that serves as a dedicated cable to our Uno.
*Disclaimer... that's the way I understand it, anyhoo. Your mileage may vary, E&OE....