PHP on Arduino, would it be possible to create a shield that could store and be able to process PHP scripting and work as a web server?
No; the Arduino is about a factor of 100 too small to be able to host the PHP runtime. PHP is simply *way* too bloated to fit in 32 kB of program memory (much less 2 kB of RAM.)
Basic OS, I'd love to know wether it is possible to create a basic OS... more like a menu if anything, press 1 to go to calculator press 2 to make LEDs light up etc
What you're describing sounds like a GUI shell, rather than an OS. The Arduino is statically linked -- you don't install new little snippets of code (like programs); you install a whole new image. Yes, you can probably fit a calculator and an LED blinker and a menu program into a single Arduino, but you'd build them all as one program (consisting of many files, perhaps.)
Network Attached Storage, nothing as advanced as a HDD but maybe an SD card or pen drive
The Ethernet shield lets you serve files from an SDcard using HTTP. It's possible that you could get enough read/write and protocol decode into a single Arduino so that you could do a WebDAV based storage server (or at least a PUT/GET based server,) but that would be a real squeeze in a regular Arduino, size-wise. The performance would also be quite slow!
Pong, a pong game on LEDs or to a TV
Pong on a serial bitmap display has been done. I don't know of any TV output shields, but they might exist. Pong is simple enough that it'll fit fine in the Arduino.
Thanks for you reply! Much appriciated!
So would there be no way to extend the memory on an Arduino to support it, or is that completely out of the question (I'm a n00b...)
And yeah, a single program that ran procedural, so, one button linked to a cacl, the other to an LED blinker etc etc.
So in terms of extensibility, is there much you can do with the Arduino or are you limited? What are the limits you can go to, could you create a simplistic computer like the ZX, or build a shield to output RCA/RGB? Thanks