[ElDiabloConCaca]

In the Mac world, there are no "upgrades." When you purchase Mac OS X "Tiger", you get the full install of Mac OS X Tiger. You can use that disk to "upgrade" a system running Mac OS X "Panther" to Mac OS X "Tiger."

When you purchase Mac OS X Server, it's a full install of the server software -- more than likely, you will install a fresh, new install of Mac OS X Server on a machine running Tiger.

"Panther," "Tiger," and "Leopard" are code names given to Mac OS X versions -- 10.3, 10.4 and 10.5, respectively. Beyond that, Mac OS X comes in two flavors: client and server. There is a Mac OS X "Tiger" client install, and a Mac OS X "Tiger" server install. So when you refer to "Tiger," you're referring to the Mac OS X codebase that is version 10.4. "Tiger" does not denote either "client" or "server" install.

"Aqua" is the window manager that Mac OS X uses -- much like "Gnome" or "KDE" on the Linux side of things. It's been a part of Mac OS X since version 10.0.

Mac OS X Server "Leopard" can be installed on any machine that is compatible with "Leopard" -- a G4/G5/Intel-based Mac with a processor of at least 867MHz and 1GB of RAM. Detailed system requirements can be found on Apple's Leopard page on their website.

In a typical setup, you'd have one machine running a Mac OS X Server flavor -- either "Tiger" or "Leopard." Then, client machines running the client flavor of Mac OS X (either "Tiger" or "Leopard") would then connect to that server.

That's just a bit of clarification on what flavors of Mac OS X are available, and how they're typically used -- it may help to post verbatim what the requirements are for both MacPractice and the X-Ray data manipulation program you want to use, and we can suggest an optimized setup to get what you need done, done.