Windows 7 can be install on a Intel Mac using Boot camp(Apple Software) or Parallel desktop etc.
Boot camp Supports to Dual boot i.e Windows 7 and OS X lion and also its not easy to swap 7 to Lion in it.
Besides in Parallel Desktop one can easy swap or switch. Also,it installs as a third party software in Mac lion.
No Dual boot, Boot from lion switch easily to Windows 7, manage folders in between them,run windows program on single click.
The Price of it is 80$ as campared to Boot Camp which is free of cost.
Buy From here Parallel Desktop
Below are screenshots:-