An easy way:

1. Copy Office 2007 source files to a network share
2. Run Office 2007 setup.exe /admin and create an MSP file. Put it in the updates directory of your Office 2007 source.
3. Define an EXE software distribution package pointing to Office 2007 setup.exe.
4. Deploy it with any Delivery Method you like. Run from source will be fast for a few machines at a time, Multicast will be slow but effective for lots of machines.
   

Another way:

The steps needed to do this are simple:

1. Remove Office 2003
2. Reboot
3. Install Office 2007

Remove Office 2003

1. Get your files in order.
   
1. If you've already got a network install point all set up with ORK, you can just use it.
2. Otherwise, you'll need to copy the CD contents to a share and use that. This must be a UNC share, not HTTP. Make sure that file system permissions are straightened out, either your machines (not their users) can download these files directly or you can pass credentials using a Preferred Server definition.
   
2. Define the package.
1. If you already have an MSI package defined for installing, just right-click it and select clone. This will take a little while. When it's done, rename it to Office 2003 Uninstall. On the Install/Uninstall page, click the Uninstall radio button.
   
2. If you don't, create a new package of type MSI and point it to \\SERVER\PACKAGES\Office2003\STD11.MSI or PRO11MSI. On the Install/Uninstall page, click the Uninstall radio button. On the Additional Files page, select all of the files in the share and click the right arrow button.
3. Define your prerequisites.
1. On the prerequisites tab, either select your existing "Has Office 2003" query, or click New. Create a Query looking for "Software"."Application Suites"."Application Suite"."Name" Like "Microsoft Office 2003".
4. Save this package definition and drag it to the public folder.

Reboot

1. Create a new text file at \\SERVER\PACKAGES\post-office-reboot.bat, containing "C:\PROGRA~1\LANDesk\Shared~1\winrestart.exe". Make sure it's downloadable.
   
2. Create a new public package of type BAT and point it at this file.
3. Go to Dependencies and select Office 2003 Uninstall.

Install Office 2007

1. Use the Office 2007 Deployment Kit to create a network install point customized to your needs.
2. create a new package of type MSI and point it to \\SERVER\PACKAGES\Office2003\SETUP.MSI. On the Install/Uninstall page, click the Install radio button. On the Additional Files page, select all of the files in the share and click the right arrow button.
3. Make it dependent on Post Office Reboot.
   

Tie it all Together

1. Go to Scheduled Tasks and create a new Software Distribution task.
2. Choose your Office 2007 package.
3. Choose a Policy-supported Push deployment method. If you use one with targeted multicast and bandwidth limiting enabled, it will take a long time to deploy the bits and start the job; if you chose run from source, you will use more bandwidth. Select accordingly.
4. Save your task, drag in a query to target, and start now.