SPCR

My brother wants to upgrade his video card & CPU in the future to most likely a Athlon X2 6000+ and HD4850 - how many amps will his PSU need on the 12V rail for the system to run? He doesn't have much else, one hard drive, one DVD drive and 2 case fans, but his current PSU is an old/cheap one that came with his case, and with only 18A on the 12V rail - too little I think but I'm not sure myself. It doesn't even have a PCI-E power connector but I have a molex->PCIE if it's powerful enough.

There are calculators on the web which can tell you this, for example http://web.aanet.com.au/SnooP/psucalc.php.

The other issue is that the 4850 is quite a hot running card, both at idle and when running games. It will need a well-ventilated case - it might be worth putting the existing hardware into a new case. Something like the Antec Three Hundred could be an economic way of doing this.

This particular case (and others) allows an optional fan at the side, and I would recommend that this option be used in view of the 4850's thermal characteristics. I would also recommend if you go this route that the optional front fans are added too. All fans are 120mm so you could pick something of the SPCR recommended list and still have a reasonably quiet but well-cooled gaming system.