explorer file size

I am using Vista-64 and found explorer.exe in three different folders. The folders are "Windows", "System32" and "SysWOD64". The file size of explorer.exe in both "System32" and "SysWOD64" are the same. However, the file size in "Windows" are bigger. Anybody using Vista-64 please tell me what is the file size in your Windows? Thx! I am tracing the trojan.

Directory of C:\Windows
11/04/2009  15:10       3,079,168 explorer.exe
            1 File(s)    3,079,168 bytes
Directory of C:\Windows\System32
11/04/2009  14:27       2,926,592 explorer.exe
            1 File(s)    2,926,592 bytes
Directory of C:\Windows\SysWOW64
11/04/2009  14:27       2,926,592 explorer.exe
             1 File(s)    2,926,592 bytes