First off, let me explain how PHP and CSS work.
PHP is a server-side scripting language. That is, you write a script, and that script runs (like any other program) on the SERVER, and the output of that script gets sent to the visitor's browser through the net. Visitors (or their browsers) never get/see/run the actual PHP code, only the output of that code.
CSS on the other hand, is just an extention to HTML. It's code, but not a script/program that has to be run. Like HTML, it's code that basically describes how to layout/show things. All HTML/CSS gets sent, in full, to the visitor's browser, and it's up to the browser to read/combine all of it, and produce a pretty web page.
The third type of "code" involved in web design (besides server-side script, and formatting/layout code) is JavaScript. Like HTML it gets sent in full to the visitor's browser, but it actually RUNS like a program, actively doing things in the browser.
PHP (or other server-side scripting languages) can be used to generate/send anything to the browser, including images, javascript, and of course html. The xepher.net newsbox, for example, is coded in PHP... on the server side, it does a few nifty things, like checks which sites are in the rotation to have their banners displayed, gets the filenames for the various banners, and keep track of view counts. Then it sends javascript to the browser, which runs it, and that javascript tells the browser to add some HTML and CSS to the page. That html and css describe how the box looks, and what images to use for buttons, and all that normal web design stuff. The javascript ALSO does the fancy stuff, like fading to new images every short bit, and when you click on the buttons, javascript in the browser tells it just to grab the next image, and replace the current one, rather than doing the normal thing of going to a new page or link.
So, long story short, you don't need anything special to view or work with CSS on your own system, so that's good, but there's no real way to simulate PHP. You can setup a full webserver on your desktop, and run things in that, but even then, it's not the same. Especially if the PHP code is using things like database access or other things that wouldn't be available on your desktop. That said, my favorite way to work on web development is directly on the server. In linux it's trival to mount a directory (via SCP) on the local computer. That is, I can have a folder on my desktop that's actually on the server. I can open/read/edit files in there just like they were on my desktop, and the second it's saved, it's already on the server, ready to be viewed/tested. Mac has several similar utilities (being based on unix as well) but I'm not really sure what to use in windows for that. I know there are things... google found me this
http://lifehacker.com/software/featured-windows-download/mount-remote-file-systems-with-netdrive-300997.php but it seems like it may or may not work these days. There's some additional suggestions in the comments there.
As for editor programs, I'm with Tickyhead here... WYSIWYG programs like FrontPage or Dreamweaver do make some things easier, but when you really get down to it, it's hard to beat human coding. Syntax highlighting HTML editors (what ticky described as "adds pretty colors") are really the way to go, but can take some getting used to before you really appreciate all their features. Quite a few of them do auto-completion and automatically close tags for you. But yes, coding things by hand does seem slower at times, but as you get better at it, you realize ways to save time/effort and automate stuff. For example, it's a royal pain to make a HUGE table with 100 lines it when you're coding by hand. In FrontPage or something, you just type in how many rows you want, and "poof" it's there. But when I code by hand, I'm usually writing PHP as well... so I just have to make one row, and tell it to loop 100 times. Not an exact example, but you get the point.
Sorry if that sounds like the grumpy-old-man answer, but if you really do want to get better at web design, it's essential to learn to do things by hand, even if you still bring in things like dreamweaver to help with certain tasks. The point is, after you learn the nuts and bolts under the hood, you'll know WHEN to use what tools, and more importantly, when not to!
