Both the PowerPC and Intel source code for darwin is freely available and can be downloaded at the address below

http://www.opensource.apple.com/darwinsource/

all versions from 10.0.0 to 10.4.9 are available

also apple’s developer tools (X Code) is also available on that page to download the source

The Safari Webkit source is avaliable along with lots more components at

http://developer.apple.com/opensource/index.html

Apple has always embraced open source from the beginning of Mac OS X. Linux/Unix users are not our enemy, Microsoft is!