Here's what you want to do:

First, open up disk utility and select your hard drive in the sidebar:

Now, click the little "Create Partition" icon. Make sure you're selecting the right drive, this is the dangerous part!

Now, lets get this drive mounted on our computer.

Click that, and then it will mount on your computer. Navigate to it and then right click on it, then select Properties. Navigate to the "Sharing" tab:

Then, check the "Share This Folder" box.

Select "Install Service".

Select "Install".

Then you will see that - enter in your password and follow the rest of the prompts.

When its done, it will ask you to install another piece of software, and then when that is done it will ask to restart your session - to do that, save any of your other work, and then click "Yes".

Come back in, and then find the directory (folder) that you want to share, and then share it like we did above (it might already be shared, I had two different computers and I had to check it on one computer, and on the other it was already done. shrug)

Anyway, to connect to it on your other computer, click the "Browse Network" item in the Nautilus sidebar:

And then find the share that we want to connect to, and then just go from there! Enjoy the shared networking goodness! :)