Ideally when you're a PHP programmer/developer you should be able to access Windows and Linux at the same time.
Depending on the number and the built of computers that you have, there are 3 ways to achieve Windows and Linux parallelism:
1. if you have several PCs, acquire two computers and install one pc with Linux and the other with Windows, then hook it up on your network
2. if you only have one PC that can support virtualization, go for this option.
3. if your PC cannot support virtualization, purchase a domain and web space installed with Linux, Apache, MySQL and PHP (LAMP)
In my case, during development or experimentation, I would opt for #2.
So what are the advantages of virtualization?
1. You could have several operating systems running without having to reboot.
2. It gives you freedom to mess up with the virtual OS environment. If you screwed up on something during development or testing, you could always rebuild the virtual computing environment. Highly recommended and effective for people who want to learn Linux.
3. You'll save on hardware cost.
Currently, I am using Sun Microsystem's VirtualBox - an open source virtualization software that runs on different platforms such as Windows, Linux, MAC OS etc.
I have installed it on my WindowsXP and Ubuntu OS (I have a dual boot PC)...since then I am one happy soul.