Windows 7 is available in Beta version and it has some bugs as well as compatibility issues with other softwares. People installed it just for the sake of curiosity and now facing weird problems.
If you are one of them and want to uninstall Windows 7 from your PC then you can use following tutorial. It will be more helpful to those people who have dual boot systems and Windows XP installed on the PC.
You should not use this tutorial if you only have Windows 7 and Windows Vista in dual boot.
Steps to Uninstall Windows 7
- Start Windows XP.
- Insert Windows 7 ISO DVD into DVD drive.
- Press ‘Win + R’ to open Run command prompt.
- Type [DVD Drive Letter]:\boot\bootsect.exe /nt52 ALL /force and click on OK.
Note: Add the name of your DVD drive in [DVD Drive Letter] field.
- Remove DVD from your drive and reboot the system.
- Your computer will boot up with Windows XP installation.
- Now you can either format the drive containing Windows 7 or manually remove files of Windows 7.
- Finally remove Boot.BAK and BootSect.BAK from root system folder of Windows XP. Don’t delete these files if you have another operating system installed other than Windows XP.
Alternate Method: Simply format the drive that contains Windows 7 files and repair your system with Windows XP installation CD for any booting errors. 
Now you can easily access Windows XP without any reinstallation of OS. If you find any error or difficulty while uninstalling Windows 7, please let me know in the comment section.