Drilling down, would take place from top to bottom, with the top node being the over system.
    The difference between a 2D system, and a 3D system, would be the tree in three dimensions, and you would be able to rotate the view, avoiding visual compression.
    Float over text would explain what each node represents, or we could vary the shape, but that might add confusion.
    At the bottom level we could display actual numbers and figures, although the float over should take care of that.

    On a more Applied level the lines would extend from the center of the node and attach to the center of it's sub node.
    The user will also have the option to follow multiple node simultaneously or individually.
    Nodes would be updated when shown, perhaps those at the current depth would have the option of polling for updates.

    A possibility for distinguishing between services, resources, and end nodes can be the above.
    My thinking on the subject is the following:

    Resources such as CPU, Memory, Disk I/O, and Network I/O should be spheres with symbols. This allows for internationalization. In Japanese CPU probably isn't spelled CPU, plus this allows, once one is used to the symbol, for quick recognition of what is being represented. It also maintains freedom of movement, by allowing us to change size and color based on other factors. You can also distinguish them at a distance. There is no confusing between M and N etc.

    For services, since the services that will be watched should be user definable, they should be spheres containing a textual label. I believe that httpd, ftpd etc. are universally exceptable.

    The following is an example of a denial of service attack through the web server. or something similar.

The top node, system name, will reflect the worst state in the system, in color code.
Service would monitor it's services to make sure that they behaved within certain constraints. Their color's would change if they begin approaching their maximum.
Under httpd are all processes running a command with the word "httpd" in the command line, one of which as a service has violated it's safety bounds, but as a process is still with in it's limits.
The blue nodes conatian process information. Information, that can only be described in one dimension, memory usage, net traffic, port number etc.
The gray sphere is a remote system, that we have no information on except that it's connected to us, and it's ip is x.x.x.x.