Problem after installing SP3 for Excel 2003.

After installing SP3 for Excel 2003, I'm not able to open Lotus 1-2-3 files. When I try to open/save a .wk3 or .wk4 file we get the following error.
"You are attempting to open a file type that is blocked by your registry policy setting".
When I googled for the above problem, I landed in Microsoft site. The below extract is from Microsoft site.

Excel 2003

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 (http://support.microsoft.com/kb/322756/) How to back up and restore the registry in Windows


An administrator can restrict the types of files that you can open in Excel 2003. This ability was not provided in Microsoft Office 2003 when it was originally released. To restrict the types of files that can be opened in Excel 2003, install security update 933666.

For more information about security update 933666, click the following article number to view the article in the Microsoft Knowledge Base:
933666 (http://support.microsoft.com/kb/933666/) Description of the security update for Excel 2003: May 8, 2007

To restrict the types of files that you can open in Excel 2003, an administrator can use one of the following methods: • Use the updated Office 2003 Administrative Templates to configure the registry on the client computer.
• Modify the registry by adding a registy key setting on the client computer. To download the Office 2003 Service Pack 3 Administrative Template (ADM), OPAs, and Explain Text Update, visit the following Microsoft Web site:
http://www.microsoft.com/downloads/details.aspx?familyid=BA8BC720-EDC2-479B-B115-5ABB70B3F490&displaylang=en (http://www.microsoft.com/downloads/details.aspx?familyid=BA8BC720-EDC2-479B-B115-5ABB70B3F490&displaylang=en)
The following table contains the DWORD names that an administrator can add to the registry to restrict certain file types by using the FileOpenBlock subkey. Additionally, the table contains the corresponding file types that are restricted. DWORD name File types that are restricted
BinaryFiles .xls, .xla, .xlt, .xlm, .xlw, .xlb
HtmlandXmlssFiles .mht, .mhtml, .htm, .html, .xml, .xmlss
XmlFiles .xml
DifandSylkFiles .dif, .slk
TextFiles .txt, .csv, .prn
XllFiles .xll
Converters All file formats that are available by using a text converter (including the Office Compatibility Pack)
DatabaseandDatasourceFiles .odc, .udl, .dsn, .dbc, .dqy, .iqy, .oqy, .rqy, .mde, .mdb, .dbf, .ade, .adp, .cub
LotusandQuattroFiles .wk1, .wk4, .wj3, wk1 FMT, .wks, .wk3, wk3 FM3, .wj2, .wq1, .fm3, .wj1
LegacyBinaryFiles Microsoft Excel 4.0 Charts (.xlc) files (Office 2003 SP3)
LegacyDatabaseAndDatasourceFiles DBF 2 (dBASE II) (.dbf) files (Office 2003 SP3)
To enable the FileOpenBlock subkey settings, follow these steps: 1. Exit Excel.
2. If you are running Excel 2003, install security update 933666 if it is not installed, and then go to step 3. If you are running Excel 2007, go to step 3.
3. Click Start, click Run, type regedit in the Open box, and then click OK.
4. Locate and then click to select one of the following registry subkeys:

Excel 2007
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\FileOpenBlock HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Excel\Security\FileOpenBlock
Excel 2003
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Excel\Security\FileOpenBlock HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Excel\Security\FileOpenBlock
If the FileOpenBlock subkey does not exist, follow these steps to create it: a. Click to select the Security subkey.
b. On the Edit menu, point to New, and then click Key.
c. Type FileOpenBlock, and then press ENTER.

5. Point to New on the Edit menu, and then click DWORD Value.
6. Type the DWORD name that you want to restrict, and then press ENTER. For example, type BinaryFiles.
7. Right-click the DWORD name that you typed in step 6, and then click Modify.
8. In the Value data box, type 1, and then click OK.
9. On the File menu, click Exit to exit Registry Editor.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
945797 (http://support.microsoft.com/kb/945797/) You receive an error message when you try to save a file type that was blocked by your registry policy settings in Excel 2007 or in Excel 2003 .

For full details check here http://support.microsoft.com/kb/922848/