Can I bypass the drop box?

I am new to the forum. I hope someone can help. I have a network with 3 macs. I just upgraded two of them from system 10.4.10 to Leopard 10.5.1. The third is still at 10.4.10.
I am trying to get everything sharing again. We used to be able to move freely into the files on other computers but now we are stopped by these dropboxes. We haven't seen these before. We want to get back to the abilities that we had before.
The computer with the older system has the icons for one of the two "Leopard" computers, but can't seem to see the other one. The two "Leopard" computers can't see anything except a drop box.
How do I get those Icons onto the "Leopard" computer desktops and get my complete network back?
Thanks in advance for any help.
Peggy

Do you see a button that says Connect As on the 10.5 systems when you try and connect to the other systems? Click it and put in the username and password of the system you are trying to network with.

Thanks but, no, i don't find that option Where exactly is the "connect to" button?