What is ntdll.dll?

[X-Man]

I have Windows XP SP3 installed on my computer. Recently my computer was visited by some virus and trojans. Now i had an antivirus program but it was now up-to-date, so i updated my antivirus program and scanned my computer. Now all the Virus were sweeped from my computer. When i restarted my computer, it refused to start. so i repaired install Windows XP and now NTDLL.DLL is shown as infected again. Can i delete this file? Is it an important file? While i observed that this file exists on my other computer too which has Windows 2000 Professional. Any help would be appreciated.

[SmirnOFF]

File description: Win32 NTDLL core component
Version : 5.1.2600.2180
Size : 0.31 MB

Details : Normally it is located in the "c:\windows\system32" for Windows XP and at "c:\winnt\system32" for Windows 2000 and can also be found in the "i386" directory of the Windows Installation Disc. It has a description as a 'NT Layer DLL' and it contains NT core kernel functions.

[X-Man]

So that means this is a necessary file for Windows functioning and i cannot delete it. I have a lot of data and no backup options. So till i find a backup option, i will have to let this virus on my computer. Any other help? Thanks!

[FaMe FacToR]

If you have the Windows Installation disc with you, you can try this : Let the antivirus to handle the file. If it is cleaned without deleting the file, its good. But if this file is deleted use the Windows Disc to get a clean copy of ntdll.dll file which will be located in the "i386" folder. Copy this file to 'C:\Windows\System32" directory and restart your computer. See what changes you see.