This is a problem that can be caused by a damaged registry key.

The Microsoft Knowledge base has an article explaining the solution to this. It can be found at http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/q170/0/86.asp&NoWebContent=1 .

I'll also cut and paste the text below.

I hope you find this helpful.

G. Ciser

(The following is copied from the Microsoft Knowledge base website and is from Knowledge Base Article - 170086)

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System32 Folder Opens When Logging on to Windows XP, Windows 2000, or Windows NT 4.0
View products that this article applies to.
This article was previously published under Q170086
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry

SYMPTOMS
When you log on to Microsoft Windows, a Microsoft Windows Explorer window may open that displays the contents of the System32 folder.

This behavior also occurs if there is a String value that contains only a single quote character (") as the Value data in the following Registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

CAUSE
This behavior can occur if a null, incomplete, or damaged entry exists in the registry.
RESOLUTION
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

Use Registry Editor to view the following two Windows registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

Verify that all the values in these keys do not contain any incorrect, incomplete, or null entries (such as "").
MORE INFORMATION
An incorrect entry in the following registry value has been confirmed to cause the behavior described above:
Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
Value: ActiveMovie File Extensions
Value Type: REG_SZ
Value Data: ActMovie.exe /Check

If the value data for this entry is null or appears in Registry Editor as quotation marks, you may experience the problem described above. To correct the problem, change the value data to match the entry above or delete the ActiveMovie File Extensions value.

This behavior can also occur if the Reminder value that has "" next to it is in the following registry key:
HKEY_CURRENT_USER\Software\Microsoft\Windows\Current Version\Run


You can resolve this behavior by deleting the Remainder value.

If you are uncertain whether an entry is incorrect or incomplete, you may want to delete all entries other than the default Windows entry. The following entry to run the System Tray is the only required Windows default entry:
Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
Value: SystemTray
Value Type: REG_SZ
Value Data: SysTray.exe

For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
177510 System32 folder opens when Windows NT starts

The information in this article applies to:
Microsoft Windows XP Home Edition
Microsoft Windows XP Professional
Microsoft Windows 2000 Server
Microsoft Windows 2000 Advanced Server
Microsoft Windows 2000 Professional
Microsoft Windows 2000 Datacenter Server
Microsoft Windows NT Server 4.0 Terminal Server Edition
Microsoft Windows NT Server 4.0
Microsoft Windows NT Workstation 4.0
Last Reviewed: 6/24/2004 (4.0)
Keywords: kbenv kbprb kbui KB170086