Can I install Ubuntu 12.04 on Raspberry Pi, model B? I need a small, cheap PC for XBMC media center and a browser to connect to my PC. I need a wifi, so I need at least 2 USB ports. I have set my eyes on Raspberry Pi, but not sure wheather it will provide. Please, provide any info on the topic, or alternatives.
Not at all. The Raspberry Pi is an ARM based computer, so you have to use a version of linux (and all software) specifically compiled for it.
In addition, the ARM instruction set is older than Ubuntu supports (see http://www.raspberrypi.org/faqs ), so you may have to use Debian which is similar to Ubuntu in the mean time.