Displaying the security tab in XP Pro can be achieved by disabling simple file sharing. You can accomplish this by opening the Folder Options applet in the Control Panel. Click the View tab and remove the check beside the Use simple file sharing (recommended) option.
However, if you are running XP Home Edition, the process is slightly different. With this edition of XP, Simple File Sharing cannot be disabled. Assuming that your hard drive has been formatted with NTFS, you can display the Security tab by booting into Safe Mode and logging in with the Administrator account.
If you frequently require access to the Security tab and do not want to boot into Safe Mode to access it, you can download the Security Configuration Manager (Intel Version) from Microsoft. Double click SCESP4I.EXE and extract the files to a location on your computer. Right click the Setup.inf file (this will be located in the location where you extracted the contents) and click Install. You will need to restart your computer once you are complete.