It's certainly possible to develop on a Windows machine, in fact, my first application was exclusively developed on the old Dell Precision I had at the time :)
There are three routes;
- Install OSx86 (aka iATKOS / Kalyway) on a second partition/disk and dual boot.
- Run Mac OS X Server under VMWare (Mac OS X 10.7 (Lion) onwards, read the update below).
- Use Delphi XE4 and the macincloud service. This is a commercial toolset, but the component and lib support is growing.
The first route requires modifying (or using a pre-modified) image of Leopard that can be installed on a regular PC. This is not as hard as you would think, although your success/effort ratio will depend upon how closely the hardware in your PC matches that in Mac hardware - e.g. if you're running a Core 2 Duo on an Intel Motherboard, with an NVidia graphics card you are laughing. If you're running an AMD machine or something without SSE3 it gets a little more involved.
If you purchase (or already own) a version of Leopard then this is a gray area since the Leopard EULA states you may only run it on an "Apple Labeled" machine. As many point out if you stick an Apple sticker on your PC you're probably covered.
The second option is more costly. The EULA for the workstation version of Leopard prevents it from being run under emulation and as a result, there's no support in VMWare for this. Leopard server, however, CAN be run under emulation and can be used for desktop purposes. Leopard server and VMWare are expensive, however.
If you're interested in option 1) I would suggest starting at Insanelymac and reading the OSx86 sections.
I do think you should consider whether the time you will invest is going to be worth the money you will save though. It was for me because I enjoy tinkering with this type of stuff and I started during the early iPhone betas, months before their App Store became available.
Alternatively, you could pick up a low-spec Mac Mini from eBay. You don't need much horsepower to run the SDK and you can always sell it on later if you decide to stop development or buy a better Mac.
Update: You cannot create a Mac OS X Client virtual machine for OS X 10.6 and earlier. Apple does not allow these Client OSes to be virtualized. With Mac OS X 10.7 (Lion) onwards, Apple has changed its licensing agreement in regards to virtualization. Source: VMWare KnowledgeBase
A lot of the answers here helped point me in the right direction, however none were suitable for me, so I am posting my solution.
I have Windows 7, which comes with PowerShell built-in. Here is the script I used to find/replace all instances of text in a file:
powershell -Command "(gc myFile.txt) -replace 'foo', 'bar' | Out-File -encoding ASCII myFile.txt"
To explain it:
powershell starts up powershell.exe, which is included in Windows 7-Command "... " is a command line arg for powershell.exe containing the command to run(gc myFile.txt) reads the content of myFile.txt (gc is short for the Get-Content command)-replace 'foo', 'bar' simply runs the replace command to replace foo with bar| Out-File myFile.txt pipes the output to the file myFile.txt-encoding ASCII prevents transcribing the output file to unicode, as the comments point out
Powershell.exe should be part of your PATH statement already, but if not you can add it. The location of it on my machine is C:\WINDOWS\system32\WindowsPowerShell\v1.0
Update
Apparently modern windows systems have PowerShell built in allowing you to access this directly using
(Get-Content myFile.txt) -replace 'foo', 'bar' | Out-File -encoding ASCII myFile.txt
Best Answer
There's no real straightforward way. You'd have to isolate most (if not all) your platform specific routines into different files and load them up after checking for platform.
Steve Yegge has some information on how he manages his .emacs file along with the actual code itself over here. One of his points is how he keeps is cross platform hackable. It's worth a read.