The other day I heard that Windows 8 will boot faster on UEFI enabled systems. At that time I didn’t know what it was. So I did a little research, but I’m still confused
I’m using Windows 7 and my motherboard also supports UEFI boot.
UEFI (Unified Extensible Firmware Interface) is the newer version of EFI which is a "replacement" for the old BIOS (Basic Input Output System).
The main difference [which is also responsible for the faster boot] is that EFI is better in communication with hardware & firmware. For example an EFI enabled system doesn't need a boot sector on the Hard Drive or can use a graphical interface with fully mouse and keyboard support.
Basically, if your motherboard supports UEFI it is already using it in it's core except for the boot options. There should be an option to enable or disable Legacy BIOS boot (consult your motherboards manual on it).
To answer your second question:
Well, there is no definite answer or at least I didn't find one.
In theory, Windows 7 is using the GUID Partition Table which is the only requirement for UEFI boot. But it is a good assumption that you still have to reinstall Windows.
Also you will have to own a 64bit copy and licence of Windows 7 because the X86 version doesn't support EFI.
of course, since the x86 license works on x64 its a non issue.....