Set the workgroup name on both computers to be the same and give each computer a different name.
Run the Internet Sharing Wizard on the main computer. Make the disk when offered and use it on the laptop.
Don't tell me - the laptop doesn't have a floppy disk!!!!
Check the management software on the main computer for the channel being used and set the same channel in the laptop.
Open its management software and tell it to look for a ad-hoc connection. Set its IP address to 192.168.0.2 and the default gateway to 192.168.0.1