Is is possible to use remote desktop to a Mac via direct cable or wireless? I develop on Windows, but I need a Mac for iPhone development.  So I'm thinking of getting a Mac mini or a MacBook for the Mac part, and connecting to it as needed from my Windows machine. A mini, in particular, doesn't come with a monitor or keyboard or mouse, so this would be the only way to use it.  

The question is: sometimes I travel and so I'm away from my network.  In this situation, is it possible to plug a cable directly from my Windows machine to the Mac and do remote desktop this way, or do both machines have to be on the same network and router and the sharing done via IP address in the usual way? Alternatively, can I skip the network entirely and remote desktop machine to machine via wireless signal?
First off, it's important to note that Apple's Remote Desktop is not Microsoft's Remote Desktop, and the two are not interchangeable. That said, you can still use various VNC products to connect from the Windows machine to the Mac. 

From there, it's standard networking. If you want to leave the Mac Mini at home, you'll need to make sure that you can access the required ports, whether by port forwarding, or by an SSH tunnel/VPN allowing you to connect to your home network. 

If you bring the Mac Mini with you, then you can easily create an ad hoc Wi-Fi network to connect them both too, in which case they will be on the same network, and you can connect that way. (You may need a monitor and keyboard attached to the Mac Mini at some point to configure this.)

Additionally, the Mac can automatically make any standard Ethernet cable into a crossover cable, such that an Ethernet cable connecting your Mac to your PC will create a network connection for the two machines, which, again, you can use as a standard network to connect from one to the other. 

The network can be WiFi, direct point to point ethernet, point to point thunderbolt, point to point firewire or over a wired switched network of any of the above carriers.