How do share a folder?

Hi! I just reformatted my computer and lost all my settings in the process, of course, and now I'm having problems setting my "shared folder" with my other computer. I already allowed file sharing, and I can see the other computer on the Network and Sharing center, but when I go click on the other computer it tells me I might need permission or that the network is no longer available. Now, the network is working fine, since the other computer can connect to the Internet through me and all the settings in the 2Wire Modem are correct, (I use ATT dsl) so, I'm totally lost about what to do... please, someone, save my sanity!!!