Other simple child-safety tips: keep the computer in a family area. This literally keeps everything in the open. He will inevitably get told about nasty websites by his schoolfriends - you need to foster a relationship whereby he feels safe talking about this with the adults at home, who can help him understand why we don't go on these sites, why we don't make unpleasant remarks about people online etc. Having a family agreement about what to do when we see something that makes us frightened, uneasy or upset will be very helpful, as again it removes the secrecy and guilt that many online paedo's thrive on.
Some experimentation will be inevitable but the family ambience, other people being around etc helps keep him safe.
Use CEOP
http://www.ceop.gov.uk/ as a source of information and support.
Kids very quickly pick up on the idea that they know all there is to know about computers and the internet and he may have peers whose parents don't lnow / care what their kids do online. Having a parent who is both interested, perhaps knowledgeable but also willing to learn new skills is a very positive learning message for the child.
You could check with your child's school to see if there are any family learning after-school clubs where kids and adults can sit together and work at computers.