how to share files between win xp and win seven

hi all
I'm trying to share some files between my Win 7 laptop (wireless) and win XP PC (wired), connected to each other via a modem/router (TP-Link 150M Wireless Lite N ADSL2+ Modem Router if it's required ) but it doesn't work! they have a same workgroup name, I can ping my PC in laptop but I can't ping the laptop in PC. I don't know what to do. in the PC i can see the laptop but I can't access it, but in laptop i even can't see the PC.
please help me, and tell me if I should add more details. thanks in advance...

Ztruker said:

Take a look here: Sharing between Win 7 and XP, see if it helps (especiall post #3 by rumpty).

Hi Ztruker
and thanks for your response, I did what Rumpty said, but at this step :

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Open the Security tab and click Edit.
Click on Add and type Everyone and then click OK.
A user icon should appear in the box with Everyone beside it.
Allow Full permission for Everyone. (This excludes Special permissions.)
Click OK.
The computer should then go through the process of setting permissions for the drive folders. The process stops half a dozen times with errors but just click Continue.
Click OK to finish.

When I click "Continue" It gives me error, this error :



I think something is wrong with my laptop, but I don't know what, please help me I'm desperate.