Can't nework 2 macs anymore

It seems that slowly but surely, macs are just becoming PC clones and the good old days of just hooking up 2 macs in your house via an ethernet cable, enabling sharing then connecting via tcp/ip are long gone.
Anyway to get to the point:
I just upgraded to snow leopard 10.6.3 on my macbook pro.
My wife has an imac running tiger 10.4 which we don't want to change as there are printer drivers etc. that aren't 10.6.3 compatible with no snow leopard ones yet available (Epson...!)
Before I upgraded to 10.6.3 on my macbook pro, we use to be able to connect to each other's computers as registered users and share files, print etc.
Since I made the upgrade, they see each other but none of the log-in and passwords work any more, going in either direction. We keep getting "You entered an invalid user name or password - please try again".
We can share via the drop box, but this is too limited.
I have followed all Apple's and a few others instructions on setting up a user network all to no avail.

Please can anyone out there give me an "idiots step by step guide" to get our macs talking to each other again.

I forgot to mention that we are also connecting to the internet via a 4 port router and thus our macs used to and still need to connect via the router.

If anyone can help, we will be eternally grateful as at the moment although we are in the same house we can only share files via email attachments!

Here are a few things you can try (thinking off the top of my head since im not infront of my mac right now).

Go into system prefrences, open your "Accounts" window.
Check to see what each computers username and password is. (delete your admin password or make each computer the same)
Open up Sharing (under System Preferences)
Select, File Sharing, Printer Sharing, Screen Sharing on each tab.
Next, Select the Networking Button (under system preferences)
Make sure both computers are on the same workgoup (ie. Home, Network, Office)
- To get here Open the Network tab ->(location set to Automatic) Select the Networking device (Airport, Ethernet, Etc....do this on both machines)
--Select WINS tab and the 2nd dialog box you should have the same workgroup in each computer. You can makeup whatever you want, Defauts are like HOME, OFFICE, WORKGROUP.... but you can type in whatever you want. This is critical in most cases for networking windows based machines.
Click "Ok" Exit out of everything

When you open your HD or system browser window, you should be able to see the opposite computer displayed i the left hand column, When you click on the computer, the following window will have 2 buttons or possibly 1 (depends on OS version)

Click on the Connect As button, and then Registered User, and input the USERNAME and PASSWORD of the computer you are trying to CONNECT TO, not the system you are on.

After that, you should be good. If screen sharing is activated, you will see the Share Screen next to the Connect As button.


Hope this helps....again this is just off the top of my head, PM me if you need more help.