I found this information on another board. This might be a solution but I don't know if it works for SQL Server 2008.

Import and Export SQL 2005 Maintenance plans

The way SQL 2005 produces Maintenance plans is very different from SQL 2000. Instead of using the extended stored procedure xp_sqlmaint to execute and the system tables of the MSDB database to store the package – SQL 2005 uses SSIS (SQL Server Integration Services) to create and store the Maintenance plans.

To Export an existing maintenance plan from an SQL Server 2005

- Click connect in the Object Explorer

- Select "Integration Services"

- Enter credentials for the server

- Open the folder: "Stored Packages" -> "MSDB" -> "Maintenance Plans"

- Right click the package you want to export

- Select Export package

- If you want to export the package to another server or edit it – using BIDS (SQL Business Intelligence Studio) – select "File system" in the Package Placement dropdown menu.

To Import or copy an existing maintenance plan from one server to another

- On the server you want the maintenance plan copied TO.

- Click connect in the Object Explorer

- Select "Integration Services"

- Enter credentials for the server

- Open the folder: "Stored Packages" -> "MSDB"

- Right Click the folder "Maintenance Plans" and select "Import Package"

- In the dropdown "Package Placement" select SQL Server

- Enter the name of the SQL server where the source maintenance package exists.

- Click the … besides the Package Placement box and select the package you want to import from the Maintenance Plan folder.

Also found a Script but have no idea how to actually make the export/import.

USE MSDB

SELECT name

,PlanXML=CAST(CAST(packagedata AS VARBINARY(MAX)) AS XML)

FROM sysdtspackages90

Note: In SQL Server 2008 you may need to use sysssispackages table instead of sysdtspackages90.