The best thing you can do so far as speaking to people about your idea is to get ahold of a non disclosure agreement (i beleive we have one somewhere you can use ill see if i can find it) before you start telling people about your ideas make sure you have them sign and fax a copy of the agreement back to you.

At least then, if they do go ahead and steal your idea you have some legal recourse to take

Now so far as registering domains etc, i would register the singlar and plural of the MAIN domain you want to use for this project.

Then you just have to figure out a business plan for the idea and select a few (no more than 4) companies and individuals to approach about it.

Regards,

Lee