ok you probably think i must be stupid but i really struggle with dilutions etc especially for primers and understanding moles and micromoles etc. does anyone know of any useful sites or books that are useful to help with these problems?

http://www.functionalbio.com/calc.htm this site has a converter..

I just use the formula M1V1 = M2V2

where M is molarity and V is volume so say you have a primer solution which is 20ng/ul and you want 30ul of 10ng/ul solution it would work like this

20 x V = 10 x 30
V = 15 ul

So you need to put 15ul of your original solution in 15ul or water to get your desired concentration.. Hope that helps

Oh and this is a good site for converting pico, nano, milli etc
http://www.unit-conversion.info/metric.html

I have found this one pretty helpful:

http://www.graphpad.com/quickcalcs/Molarityform.cfm

Although, i find it best to do the calculation yourself too, like the way Tricky suggested, just to confirm your result