Software Deployment

Use the Office Customization Tool (IIRC, "setup /admin"). One of the options is to remove previous versions of Office. It's all thoroughly documented on TechNet.

BTW, I wouldn't recommend GPO to install Office 2007/2010. You will very quickly find a crowd round your desk, all brandishing nooses, complaining that "wasting half a day to install this junk" isn't a productive way to spend their time. Also, you cannot pass arguments to the GP package, unless you use startup or login script. If you have no alternative, fair enough, but if you do (SCCM? Radia?), use it.

Thanks for the hint! That helped me a lot!
We only use GPO.. So I have to get it work with that..

I've used the Office Customization Tool to creat a MSP file but it only works for the setup.exe and not for the MSI file.

What can I do so that the MSI also takes the settings from the msp file?

Because these MSPs aren't MSPs in the traditional sense, you can't use them in the traditional way. I spent a good deal of time at my last client trying to work out how to deploy an MSPed install via GP but, given the (relative) simplicity which SCCM afforded, gave up.

Okey..
I think I'm going to make two different GPOs. One that installs Office 2007 and one that uninstalls Office XP.

Thanks a lot for your help!

If all you want to do is select the app and pass in your serial number, the default install is fine. However, the only way to get customisations into Office 2007/2010 - not just the removal of older versions - is via an MSP. How are you going to install different languages, for example? What about disabling features?