LAN problems

Okie, I have 3 compys runner connected to the internet with one router. Two of the computers can connect to the WAN and the LAN and one of them can only connect to the WAN but not the LAN... What this means is that two computers can communicate with each other while the other one cant... But they can all connect to the Internet. Whats wrong? Can someone please give me a solution?

All 3 in same work group? What OS is each? Each system have a unique computer name that is not the same as any user name among the 3 systems?

the OS shouldnt be a problem, xp is backwards compatible w/ almost all of the other 9x's. they should however be in the same workgroup and should have unique names. just becasue one is on wlan (btw it is wlan wireless local area network] and wan is wide area network, large geographic distance0) i have 3 lans and a wlan all talking and sharing, it wasnt much of a problem. they all have diff OS'es going all the way back to 95. all that has to be done is they have to join the same workgroup, and have to have some folders shared so that files can be shared.

OS can be an issue with a mixed lan that includes Win9x/win2k and a master browser issue.

all three computer systems uses Windows XP

2 of them uses XP HOME and the problematic one uses XP PRO

same workgroup, all different names.

While all computer names are unique, are your user name(s) and password(s) set up identically on each so they have the same user(s) accounts listed? You created/defined "share names" for shared drive (not the default C$ share) or folder(s) on each:

Folders have been shared with proper share-level permissions, e.g. full control -> everyone?
Folders have been set with proper NTFS-level permissions, e.g. full control -> everyone?

Have you disabled Simple File Sharing on the Pro one? In Services, Local Users and Network TCP/IP Advanced properties of each:

Workstation service is running on each?
Server service is running on each?
Guest account is enabled?
Netbios over TCP/IP enabled?
Wins setting blank?

alright > < guess i'll check all those first.... I'll post again after i checked.