How to connect a Mac OS X and a Windows XP machine, in order to have a PHP+MysqL application running on Windows but with browser and usage from Mac OS X?

If I understand the question correctly the easiest way would be to have the two computers be on the same network (using the same switch or wireless router), then set the default gateway on the Windows machine to something else than the internet router. Since communication between the Mac and the Windows machine won't go through the gateway they can still talk, but the windows machine will just time-out every time it tries to access the internet. You might have to set the TCP/IP settings manually for at least the Windows machine, but this should be quite straight forward. (You can also install a web proxy on the mac, then configure a web browser on the Windows machine to use the proxy, that way you can still access the internet through that browser, but no other application will have access.)

This should be pretty straightforward with just a router and two network cables (or wireless network cards). Connect the router to the internet, and connect the two computers to the router. Each computer will have an IP address. Then:Set up and configure XAMPP on the Windows machine (including allowing connections from addresses other than localhost).Configure the router to deny internet access to the Windows machine.Open the Mac's browser and connect to the Windows box by IP address (e.g., by putting "http://192.168.0.105" or whatever the Windows box's IP address is into your browser's address bar).

"Your answers may include" makes it sound like a homework question or something. You need - well, what Doofus says, to be honest. But to get silly for a moment: 1) Turn the Windows machine into a VM, and run the Windows VM on the Mac, with no routing to the outside world. This has the same problem as Doofus' solution - if an attacker compromises the Mac, they can use it as a stepping stone to attack the Windows box. 2) So what we really need to do is protect the Windows machine from the outside world and a compromised machine on the local network. So we do everything Doofus said, but we also shut down the Windows machine so it only listens on port 80 (software or hardware firewall between it and the rest of the network), and we tell Apache to only Listen to the IP of the Mac. If XAMPP doesn't come with suhosin, throw that on as well, because, what the hell. But by taking the Windows machine off the network, you've made it hard to install security patches for your WAMP stack. You're going to need to figure out a way to make sure they get applied. Also, what's the lead time between a security patch being released for Apache, and it being available in XAMPP? If it's more than a few days, you might want to dump XAMPP and go for bare installs of Apache etc. Another approach would be a VPN... Client-side certificates on the Mac in addition to locking down Apache to a single IP... HTTPS on the Windows machine in case someone compromises the router...

Thanks for all the answers, they all seem good and it's hard to choose which one to mark as best. Leon: it's not a homework question, I was really asking for help on this real situation - so thanks for your nice suggestions. If it's correct, at the moment I like very much the one from Baron Humbert von Gikkingen, because it seems easy/quick, while effective. And no, accessing the internet is not required on the Windows machine, but thanks for the bonus suggestion too.

What's your motivation for wanting Windows isolated from the Internet? Are you (a) trying to protect the Windows box from attacks originating outside, or (b) trying to stop anything running on the Windows box from connecting to anything outside, or (c) both? Because if all you actually want is (a), and the Windows box is not accessible to teenage sysadmins inside your house so you can be sure that there's nothing running on it that's going to use uPnP to open any IP-facing ports on your router, then an ordinary NAT router between your LAN and the Internet is all you need. No special configuration is required, and you probably don't even need to buy a new router as most modems include one.