One quirck I just noticed is that when you try to change a share name on Windows XP Home it will not let you. You need to untick the checkbox to share this directory first and apply it. Then right click on it again to go to properties where you can setup the share again...
 
Also note this:
If you want to share files across a network and you want to give specific privileges to different people the best thing to do is to setup a domain. If you cannot setup a domain you can make a workgroup (just type a name for it in the network settings). To share files across the network it is important that you use the same usernames and passwords on the accounts on all PCs. So if you have an account on PC1 and on PC2 you need to use the same account name and password in order to access files on the two PCs. Please note that you can change your account name but that may just rename the label. If you need to rename a user it is probably best to create a new user with the new name.