Hi first thing i wanna say that this would not be a good thing or an unprofessional behavior if you try to leave your job like this.
See you are on leave now which implies you are supposed to join them back on Feb 01, 2013 (After completion of your granted leave period) but as you are now planning to quit because you got another good job offer which would not be acceptable. If you found another good job, you supposed to resign first and have to serve a notice period before your leave.
I would say, this would be a totally unprofessional or against the ethics if you'd take this step or leave without serving notice period.
Solution: You can go to your employer (Tomorrow, Feb 01, 2013, Join them as you have completed your granted leave period) and speak/request to your Boss/HR Personnel that you are not supposed to join them back with a valid reason and request them to relieve you but in that case this is totally depends on your Employer/Your Boss. By convincing them, you can only take further step to join other employee otherwise they wont give you relieving/experience letter and other due or say exit clearance that would certainly be required to join new employer and they will ask you to furnish these documents or can get this fact by Background check anytime.
Now you can understand the situation where you are and can see in future.