Computer freezing

[Hitman]

Dual channel doubles the band width of your ram. So it is twice as fast.

on AMD systems dual channel wont provide a 100% increase in speed. its more like 5% at most.
if you can afford it then get 2x 512mb, if you cant just get 1x 512mb then get another stick later when you can afford it.
also get DDR400 or DDR 433 as this will allow for overclocking headroom and will also alow you to run a 400mhz bus processor in the future