He can use both. It really depends on how much hard drive space he wants to dedicate to Windows. Bootcamp will take the hard drive and divide it into two partitions -- one will run Mac OS X, and the other will run Windows. When he starts up, he can choose whether it will be a Windows or Mac machine. When he boots into Windows, it is a full Windows computer and runs at full speed. All the memory and processing speed is devoted to Windows.