play game together does not require a lot of things as you listed. it required that all computers on the network can see each other and able to access the shared files if the game installed locally. because WinME and Win98 can only access FAT and FAT32 while Win W2K and XP can access both FAT32 and NTFS, therefore, make sure that if you're running a mix windows-base environment you should use one File System such as FAT32 for all computers on you network.
As said, the computer hosting the game should grant sufficient access to other computer accessing it. Such accesses are: Execute, Write, Modify, Read... if you only have Read access then obviously you cannot run anything.
I hope this will help you somehow. Just consider that, people who play game on the internet do not have the same hardwares configuration.
Most of the time, it is access problem.
so good luck to you.