I don't know the Mentor ADSL router but I did a quick search on google and found these; click here click here
If you do the same, you will find many useful titbits. These forums are also a good source.
Wired networking of 2 PCs should be simplicity itself, so nothing else to be considered until you have a go and hit problems when we can help again.
While you are waiting, decide on a unique name for the Workgroup which both PCs will belong to, as well as names for each.
To set these, click on Control Panel> System> Computer Name>