Hi I have 2 computers 1 has xp and other vista and both connected to internet through a wireless router. I want to create file sharing between them but in xp it's a bit difficult. I try to ping the other computer but it does not ping. Have created like a small network to communicate them with each other but it doesn't works. What should I do ?

Is that router DHCP enabled. If you can try to make the two into a workgroup & enable file & printer sharing in XP ! & simply make one default gateway of the other,carefully mind your internet settings!

Also make sure that if you are using XP SP2 that your Firewall is not blocking it and that you are on the same workgroup