Thank you 2xg.
Your suggestions work (almost).
The File & Printer Sharing settings on Win7 system are the same as your link. Then I had firewall turned off. I followed the instructions to turn on Netbios in XP. Now I can ping successfully from Win7 to WinXP. (Never had any problem when ping from WinXP to Win7)
I restarted the firewall on Win7. I can ping WinXP. However, when I restarted the firewall on WinXP, Win7 cannot ping WinXP.
How do I overcome this firewall problem on WinXP? Should I changed some settings for Services or ICMP on the Windows Firewall->Advanced->Local Area Connection page in WinXP?
Ultimately, I would like the firewall enable on WinXP and still be able to communicate with Win7 system.
Also, before I reinstalled the WinXP OS on the laptop, I was able to share files and folders between these 2 laptops. The File & Printer Sharing Settings for Win7 are the same as what your link has suggested. But when I clicked on my WinXP on Win7 (even with the firewalls turned off), on the Win7 system it said "Windows cannot access \\MyWinXP" where MyWInXP is the name of my XP system. Can you offer any advise?
Thanks in advance.