optiplex issues

The school that I work recently had some Dell Optiplex systems donated.
They appear to be from arouind 1996 or 1997. When they arrived they all had
Windows 95 on them and I have changed them to 98. When I tried to access
the Internet with one, it said it could not find a connection. I had
plugged the ethernet connection into the port, but upon reboot I got a
message saying that it had detected new hardware PCI Ethernet Controller,
but would look for the drivers. It could find any and I don't have the
original software. I went to the Dell website and found a couple of
potential drivers, but had no luck when I tried to install them. I then
opned the machine with the intent of putting another netcard in, but there
appears to be bar of some sort blocking the heads of the screws near the
slots. It looks like the only way screws can be removed is by some very
thin wrench. I want to be able to get in there, because we have a few other
computers that need sound cards. When I shut the computers off and
rebooted, I got a message saying that this computer has been opened.
Anybody out there that can help me with all of this.

--
Nate Rosenthal