Is Windows 7 a part of xp?

No, Windows 7 is Microsoft's New Operating system.

There is also Windows Vista before Windows 7 but newer than xp.

The operating Systems go like this, from oldest to newest.

Windows XP

Windows Vista

Windows 7

Windows 7 is still currently in Beta stages and have released a RC (Release Candidate) of their Windows 7 Ultimate. Windows 7, in some versions, has a capability to run in windows XP mode, this may be what you are referring to.