Namecoin name_new fee for already taken
Maybe a little bit late, but for everybody who is interested, the easy command to check if a name exists is simply:

&gt; ./namecoind name_show d/&lt;name&gt;


It will return some informations should the name already be registered, or it will return 

error: {"code":-4,"message":"failed to read from name DB"}


if the name doesn't exist.