How can I power this micro pump
USB without logic attached can source 100mA max @ 5V. Your selected pump will not work. If you select a type that requires &lt; 100mA and accepts 5V, you'll have the problem that your pump motor will induce EMI on the 5V lines that run directly into your PC. You'll need some filtering too, otherwise your PC will probably start to do wierd things every now an then.

I'd go for a mains adapter of an old mobile phone you're no longer using.