I once encrypted a folder in my windows xp system so that the other Users cannot access it. Now I've reinstalled XP and when I try to decrypt or open the file I'm not able to access the file. Please help me to recover the file.

I am assuming that you used a password of some sorts, if so then the password does not work then?

I think the password would have been stored somewhere within the computer so when you reinstalled the os you erased that as well.

Question what encryption program did you use to encrypt it? If it is commerical software best suggestion would be to get suppot from those who created and how you can decrypt it.

I encrypted the folder using the Windows XP encryption feature. Right click on folder and select Encrypt from the Advanced options. It is sored in NTFS partition

That will be a problem I think, because Windows XP uses also the machine ID in the encryption.
Do you have a drive image of your previous windows install, if you have that restore it on (another disk).
Place your current disk as slave together with the new disk, and then it could work.

Before reïnstallation you should have made a backup of your encryption key
(http://support.microsoft.com/kb/241201/EN-US/)

Most likely it will be a 128 bit key (or more) , so it takes a few 100 years to crack it.

i have my important data please help me i cant loose it.

I suggest you get a hold of Microsoft or a very good computer hacker to crack it because if you can't recover it from normal means then that folder is lost.

So get a hold of M$ first see what they can do. now if it cost you more then free. then find a good legal hacker to crack it for you.