I have promised my pre-teen son a PC to play computer games on. (I am certain I shall regret this, but a promise is a promise.) Can I just go into a shop and buy the best gaming PC? What do I need to look out for? Henry, Discovery Bay DQ: I am a great believer in establishing trusting relationships with shopkeepers. It does not matter if you want to make investments or buy iPods, you will benefit from buying from a reliable merchant. I get nearly all of my computer equipment from one source, whose views I trust. Over the years, the shop owner and I have become good friends. You would be better off going to a shop that has been around for a while; you'll be able to ask all the questions you want and can expect a thoughtful response. Meanwhile, check out websites that specialise in gaming personal computers, such as extremetech.com. The best gaming machine will most likely be the one built to specification. Here are a few pointers: purchase as much random access memory (Ram) as you can afford; obtain the largest-capacity hard-disk drive; put as much memory in the video card as you can; and get the fastest CD-Rom or DVD-Rom drive available. There are other considerations. The choice for the powerful central processing unit (CPU) is between Intel and Advanced Micro Devices; their chip designs are similar. ATI Technologies and Nvidia compete as to which has the best graphics processor card. Needless to say, not everybody agrees on what 'best' in graphics processing means. Does it refer to resolution, speed or colour? Just remember: whatever you buy today will be obsolete tomorrow. If you want to get serious about overclocking - the process of forcing a CPU to run faster than it is supposed to - you will need help from websites such as overclockers.com. Be careful what you do next. I hope your son appreciates all your efforts. You described previously how to share an address book on a Macintosh computer with other systems. I have a different problem: I want the same information on my Windows-based desktop computer at home and a MacBook Pro at work. Can you help? Name and address supplied DQ: The easiest way to accomplish this task is to use the .Mac online service offered by Apple. You must obtain a .Mac account, which is not expensive. Once you have that, open your Apple computer's address book and go to Preferences. If you click on General, there will be a check box second from the bottom that says: 'Synchronise my contacts with other computers using .Mac.' Click on that then click on the .Mac button. You will be taken to .Mac, where you can click on the items you want to synchronise (Address book is one of many). If you don't have a .Mac account, click on File then release the mouse on 'Backup address book'. The file this creates can then be read into the address book program of another machine by clicking on 'Revert to address book backup'.