Microsoft Outlook 2003 and Microsoft Outlook 2007 have a larger overall size limit 20 gigabytes (GB) for the personal folders (.pst) file than the .pst files that are in the earlier versions of Microsoft Outlook such as Microsoft Outlook 2000 & XP. In Outlook 2002 and earlier, the .pst files are in the American National Standards Institute (ANSI) format, and the overall size has a limit of 2 gigabytes (GB) only. Unicode PST file has the overall size limit of 20 GB. Just to avoid corruption due to exceeding the size limit of 2 GB imposed on ANSI PST file, you need to convert your ANSI PST file to Unicode PST file to enhance the size limit to 20 GB. Convert Outlook 2000 to Outlook 2003 using PST Conversion Tool. Suppose you have created your PST file in Microsoft Outlook 2003 & 2007 and you want to open it in Outlook 2002 and in its earlier version. Outlook 2000/2002 will not allow you to open the PST file and results in error as "Properties for this information service must be defined prior to use". To open the Unicode PST files in Outlook 2000/2002, you need to downgrade or convert the Unicode PST to ANSI PST file using PSTUPGRADE. Do not use PST Upgrade Tool to convert Converts oversized 2GB ANSI PSTs that Outlook cannot open to Unicode PST file. While converting Outlook 2000 to Outlook 2003 you must have Microsoft Outlook 2003 & 2007 installed with a valid configured profile. Open your Outlook 2000 PST files in Outlook 2003 with Outlook 2000 to Outlook 2003 converter Software. Software runs smoothly in Windows XP/2000/2003/Vista Operating System.