Before giving any details I have to give you this warning: Share ONLY directories that really have to be shared. Remember that sharing a directory shares everything inside it, including other directories. Never share the root (\) of a drive because that opens up the entire drive to potential hackers.
Now the details. First, you have to share the directory. I don't remember if the built-in SharedDocs directory on XP machines is automatically shared on the network or not. On the machine the directory resides on:
In Windows XP:
1. In Windows Explorer (My Computer) on the desktop machine, right-click on the drive and select Sharing and Security.
2. Click the Sharing tab.
3. Click the warning link to proceed to the sharing tab.
4. Click the Share This Folder On The Network checkbox.
5. Click OK.
In Windows Vista:
1. In Windows Explorer (Computer) on the desktop machine, right-click on the drive and select Share.
2. Two different paths now arise. If you created this directory, you should see a dialog box that says Choose People to Share With. If so
a. In the list box, select Everyone.
b. Click Add.
c. Click the Share button.
3. If instead you get a Properties dialog box,
a. Click Advanced Sharing.
b. Check Share This Folder.
4. Click OK.
Now it's available to be read from other machines on your network. On XP machines:
1. Click on My Computer.
2. Click the Folders button to display folders in the left-hand pane.
3. Click My Network Places.
4. Click Entire Network.
5. Click Microsoft Windows Network.
6. Click your network.
7. Click the machine you shared the directory on.
On Vista machines:
1. Click on Computer.
2. Click on Folders.
3. Click on Network.
4. Click the machine you shared the directory on.
Note: It may not show up here immediately, in fact, this has been the most frustrating part of sharing files or printers for me. Sometimes, restarting the machine with the directory seems to help this along.
If you expand the other machine's entry, you should now be able to see the directory in the list. You can click directly on it to open it, or you can go up to Tools->Map network Drive and set up a link to the directory that comes up whenever you log in.
If the above steps don't work, you may have a firewall issue where a firewall rule is preventing Windows Printer and File Sharing.
Good luck.