Silhouette

Hello, newbie here! I have a picture with multiple people in it, and I want to select one of them, and blank out the rest.

I'm using PSP7 and thought it might have something to do with masks, but it didn't do what I thought it would. Can anyone please help?

Alternatively, if this is too difficult to do in PSP7, I do have photoshop 7 as well, but I prefer to use PSP.

Thanks in advance!