You'd be better off with these as they're mounted on the little stars: http
![/ :/ :/](/images/smilies/ipb/confused.gif)
/www.ebay.co.uk/itm/6X-1W-HIGH-POWER-LED-Star-White-120LM-140-DIY-light-/270705992381?pt=LH_DefaultDomain_0&hash=item3f0755a2bd
I'd fit heat sinks to them too, just to stop them from getting too hot, working out the voltage required is easy, take the maximum operating voltage of the LED, and multiply it by the number in the circuit, so for example with the LED's I linked:
6*3.6V = 21.6V the minimum operating voltage is 20.4V, so you'll want a power unit that puts out 24V as the LED driver generally runs at about 1-2V too. The LED's draw 350mA of current, so your driver will need to match this in order for them to work, if you provide them with too much current they'll burn out.
Look for 10 LED's if you can get them, it gives you a reserve then should you get any duds or damage any.
Here's a suitable driver:
http
![/ :/ :/](/images/smilies/ipb/confused.gif)
/www.ebay.co.uk/itm/1w-LED-Driver-MBI6651-Light-Lamp-350mA-PWM-DIM-/250894393045?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3a6a789ed5#ht_4886wt_957