From personal experience, it is best NOT to have your CPU (or GPU) overclocked when installing Windows.
Once you have it installed, you can mess around with overclocking all you want.
But, leave it (and the memory) at stock speeds until you get the installation done, all Windows Updates applied (including Win7 SP1) and all settings configured.
Also, once you have that done, I would strongly recommend that you use Macrium Reflect (free edition) to create a backup image of your installation. That way, if things really go bad during overclocking attempts you have a working version to go back to.