What does this dll do?
This dll contains Internet-related functions used by Windows applications.
How To Restore it:-
Use the Recovery Console from your XP CD and then use the EXPAND command to copy a replacement for wininet.dll to \Windows\System32Boot from the Windows XP installation CD-ROM (make sure your primary boot device is the CD-ROM drive;change in the BIOS to do that),then use the EXPAND command: expand d:\i386\wininet.dl_ c:\windows\system32\wininet.dll (where d:=your CD-ROM) Then type EXIT and restart the machine.
Description of the Windows XP Recovery Console