What version of Outlook are you usging ?
If you are on 2003+, you could create a new data file with the new format, which doesn't have the 2 GB limit, and import your messages from the old file.
To Create a new data file:
1. On the File menu, point to New, and then click Outlook Data File.
2. To create a Microsoft Outlook Personal Folders File (.pst) that offers greater storage capacity for items and folders and supports multilingual Unicode data, click OK.
3. In the File name box, type a name for the file, and then click OK.
4. In the Name box, type a display name for the .pst folder.
5. Select any other options you want, and then click OK.
The name of the folder associated with the data file appears in the Folder List. To view the Folder List, on the Go menu, click Folder List. By default, the folder is named Personal Folders.
to Import items to the new data file:
1. On the File menu, click Import and Export.
2. Click Import from another program or file, and then click Next.
3. Click Personal Folder File (.pst), and then click Next.
4. In the File to import box, specify the path and file name of the newly created .pst file you want to import.
5. Follow the remaining instructions in the Import and Export Wizard.
If you are on 2002 or below, you could create a new file by using the above procedure, and then move some 'old' messages to the 'historic' file to free some space.
I would suggest one other change. Your archived file is called archive.pst. When you use auto-archive it will always archive to that file. To create a new archive file you need to right-click on the existing archive folder on your folder list and close it, then close outlook. Navigate to the folder which has this file using windows explorer. You need to change your folder options to view hidden folders then navigate to C:Documents and Settings(your profile name here)Local SettingsApplication DataMicrosoftOutlook. Rename your existing archive file to whatever you want leaving the .pst extension the same so you can still open it. Next time Outlook archives using the auto-archive feature it will create a new archive file. As Carlos says, if this is Outlook 2003 then the new file will not have a 2GB limit. You can have both the old and new archive folder open at the same time in your Outlook, but they will both be named "archive".