@OP:
This is a Mac forum so don't be surprised if the answers beyond this focus in that specific direction. Your question seems generic, as if you don't know where you are right now, a Mac place. Sorry, but that's how it comes across. Nevertheless, I have good advice for you, specifically
enterprise solutions since the other respondent covered the more basic setup:
Server
if you have rack space, get the
Xserve blade which serves Mac, Windows, Linux clients out of box and under one license. It also supports Active Directory and Xserve for your Windows IT environment. Otherwise for desktop style look into
Mac OS X Server software run on the Mac of your choice or Xserve, such as the
Mac Pro which is a powerful machine for network usage. If you choose to use a Mac running Leopard, install
MAMP Pro which will install MySQL, PHP and Apache for you under one simple client. If you opt to go Linux, I suggest Red Hat or CentOS, the latter is very stable and commonly used on VPS platforms. The advice to "avoid Linux" is not shared by me or likely most others, and you should ask that user to validate their comments with benchmark tests and facts, not just personal experience. There is a reason Linux is the most popular open source OS platform in various flavors.
Development
Buy
RapidWeaver4 for Mac as a low cost alternative to DreamWeaver, it supports all you mentioned in terms of code integration and WYSIWYG. The rest involves the usual Mac tools,
BBedit for HTML/text editing and
pick an FTP client from this list or just use terminal mode or publishing features in RapidWeaver. Mac has numerous clients for version control such as
Versions which is SubVersion for Mac OS X and works with any diff tool.
Networking
The answer to your last question depends on what you setup as the main server, distance and budget.
General advice is found in this topic which includes screenshots on setup on Windows and Mac, how to work with AD and how to share folders.
-jim