The computer is in the store right behind the mascot in the mall - when you go in there, pick to buy furniture. Then up on the top right you should see different categories like bedding, electronics, etc. Cheapest computer is 15,000 and lets you practice characterization or technique and play video games... and watch porn. ;)
The more expensive beds just raise how much stress you lose when sleeping, so I usually don't bother with those, but when you get more money you can eventually also buy a shower or tub there (that raises singing) and a TV (that raises knowledge).