Make sure both machines are in the same Workgroup.
Make sure each machine has a unique name.
Make sure any firewalls for the duration of setting the network up, are disabled.
Make sure each machine has an identical user profile - in other words, if you're Sam on computer one, with a password of Saturday, make sure there is a user on computer two that is Sam with a password of Saturday.
Once you have checked all this, post back with the result please.