The PC has to be able to see something shared out, or it won't even try to share. You have to explicitly share a drive/folder on the Mac for this to work.
BobW's suggestion probably won't let you see the Mac from the PC, though it should let the Mac see the PC. Since you mentioned elsewhere that your PC is running WinXP, I now have to ask which version. XP Home is lacking in the serious networking capabilities that are part of XP Pro, some of which are needed for the two-way connection you appear to be looking for.