Control Panel\All Control Panel Items\Network and Sharing Center\Advanced sharing settings
copy and paste this to your root explorer, like how you would type network address on ur IE/CHROME/ETC.
then check on the very bottom to have "password protection" turned off. save, exit.
make sure you share the folder, allow "EVERYONE" to access the folder on the security tab,
after you share folder like you said, on the properties windows, find the security tab. there, on the first window, if you do not see "everyone" you must add it.
to do this
1. click "edit" tab
2. click "add" tab on the new window
3. click "advanced" on the bottom
4. click "find now" on the right middle section
5. when the bottom window pops with a list of names
6. find "EVERYONE" double click the name
7. click "ok" and you are back to the original folder properties window.
8. From there, which you should now see "everyone" added, you can set to read only / full control and etc.
9. Click "ok"
Now get your XP comp that is within the same LAN,
find the windows 7 computer on the "My networks"
---If you removed the password and shared correctly, you will see the folder in which you shared and gave security to in the windows 7 pc (my networks), and password will not be asked.