First, if you are using Windows XP Home, you have to make sure to enable file and printer sharing. On windows XP Pro, this is done automatically when you join the domain. The other thing you have to do, is find the folder that you want to share
lets say you have a folder on the C:\ drive, named SharedFolder.
You must right click that folder and go to the sharing tab at the top, and select to share, and then you have to select a share name. remember the share name! For this example, we'll call it SharedFolder.
Now, you want to right click on my computer and click properties. go to the computer name tab, and make sure (if it's xp home) that the workgroup name is set, the default should be MSHOME. Now what you have to do, is go to your laptop. From here, again double check the computer name tab and make sure the workgroup name matches the one on your desktop.(Again, making sure that file and print sharing are enabled.) Now, on your laptop, right click my computer and click map network drive. from here select a drive letter(doesn't matter what you pick as long as it isn't already in use, because this isn't a physical drive, it's a virtual drive: ie. not on a separate partition). for the path name you type this: \\server\share\
is the name of the desktop computer, not the workgroup.
and where \share is the path and name of the folder you shared on the desktop.
So in your case, if your desktop computer's name is desktop, your path would look like this:
If you have any questions, let me know.