In order to make a PC keyboard more comfortable with a Mac you can make some changes in the keyboard maping, like swapping the Alt (Option) and Windows (Command or Apple) keys.

A easy and simple way to do this is using DoubleCommand, DoubleCommand is a free foftware for Mac OS X (a kernel extension) that allow you to remap some of the keys.

DoubleCommand have the follow features:

• Enter key acts as a Command key
• Enter key acts as a Control key
• Enter key acts as an Option key
• Enter key acts as an fn key (partial support, cursor keys only)
• Command key acts as an Option key
• Command key acts as a Control key
• Option key acts as a Command key
• Control key acts as a Command key
• Swaps Control key and Option key
• Capslock key acts as a Control key
• fn key acts as a Control key
• Swaps numpad . with numpad shift+.
• Shift + Delete acts as a Forward Delete
• Disable Command and Option
• PC style Home and End keys
• Backslash (\) acts as a Forward Delete
• Swap function key behaviour on new 'Books
• Disable Capslock
• Enter key acts as Forward Delete
• Caps lock acts as delete

original portuguese version here