To Snake2715, you've almost got it. To make a new PSN account, all you have to do is first make a new profile on your PS3, then use the Sign Up option under Network. You don't lose anything at all and your first profile/account keeps everything it has. Your new profile will even show all the stuff from your other profiles (since all that stuff is still on the same PS3) but the new PSN ACCOUNT will be completely fresh, meaning it won't have anything in its download list. For that reason even if you downloaded a game in your first account, if you send someone to your second account, it'll look empty unless you've downloaded something with it.
It's made this way so that if say you and your brother are using the same PS3, you can each have your own account with your own billing info and own download history. We're just using it to get extra trades.
And just incase anyone's wondering, any new accounts you make can have the EXACT SAME information as any other accounts you've made. The only thing that has to change is the e-mail address. Billing info, names, addresses and all that can stay the same.
Also, when I say 'Profile', I'm talking about the User List on your PS3. So yeah, you'd be making a User called darken if you wanted to trade with darken (You can name it anything you want but it helps keep track of who you've shared with if you name it their PSN names).
As for deleting the user/profile accidently and having your stuff not work, you'll need to get in contact with that person and the safe way is to redownload everything you've downloaded from him/her all over again, all the way through. Just make sure you delete the non-working stuff beforehand, since yes it'll still be on your drive, it'll just give you an error if you try to run it.