How to check whether your code environment on Windows or on Linux or other OS

right now, i code custom wordpress theme and testing it in xampp windows XP on apache server. But as long as i concern, there's no wp build-in function to identify the code environment. Is there's any PHP build-in function to identify such thing ? for the record, what i want to code need to read a directory. in my apache (in windows), the path will be c:/xampp/htdocs where apache on linux will be \somepath\somepath\ so, is there any code solution to know what is the OS environment without i have to retrieve and compare the path ? i hope it will also work on other OS with other webserver then APACHE such as IIS