Hi ...
I too totally support Khao Lak .... i would recommend a live aboard trip to similian islands. I dived with liquid adventure on their 3 day / 3 night live aboard ( they are the only ones who were offering richlieu rock dive in the 3 day dive package )
you can check them out at http://www.liquid-adventure.com
As for reaching from bangkok .. you can get lots of overnight buses ( we flew directly into phuket from malaysia and from there khao lak was 100kms ).
Hope this helps
Akshat