Problem networking - winXP, cable internet

[Laztrezort]

I have two computers, both winXP, both connected to the
internet via Cox cable internet, each computer getting
assigned its own Ip address. The internet works fine for
both computers, but I cannot get them to network (share).
I can ping fine between the two systems using using the
IP addresses given (ip xx.xx.xx.xx), but it doesn't work
using computer names (ip computername). Yes, NetBIOS is
on both systems, and each system has DNS servers that also
ping. Also, I cannot map a drive using either IP
addresses or computernames. There are no (known)
firewalls installed on either system. I have done all the
basing troubleshooting, and I am at a loss. If anyone has
any ideas I'd greatly appreciate it.

 

[Laztrezort]

I forgot to mention one thing -- my computers obtain
their IP addresses automatically (i'm assuming from my
network provider). However, I noticed that one computer's
subnet mask is 255.255.254.0 while the other is
255.255.253.0. I don't know if this is a problem or not,
but I thought I'd mention it.

 

[DenoxiS]

You said you tried all the troubleshooting, does it include the Windows XP's
built-in firewall? It gives this kind of troubles.