Office 2007 - I messed up! Help!

Sorry I posted this in Tech Talk instead of Tech Help. Mods? Can I get ported, please?
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Ok, I bit the bullet and bought Office 2007, even though I was perfecty happy with Office XP. But if people keep sending me docs in 2007 -- well, you get it.

My laptop already had Office 2007 pre-instaled so all I had to do was type in the product key, but when it was over I found the whole programme was in German (I bought the laptop in Germany) and I wanted it in English.

So, clever me, I decided the thing to do was de-install the German Office 2007, and re-install it with my shiny new CD. I did that.

And since then everything has gone haywire. The damn thing uninstalled my old Word programme as well! And all my Word docs have gone. (It's OK, I have backups).

Now, it keeps trying to install Office XP again and again and again. It prepares to install, trhen asks me to put in the disc (which I no lonmger have) and when I cancell the installation, it just pops up again as a new window. I tried using the new 2007 disc, but that doesn't work either. In ither words, I've lost Office XP and it won't install Office 2007!
When I use the disc it starts up with a message saying "preparing to install Microsoft Office XO Standard for Students and Teachers" which is the programme I originally used. It never even gets as far as asking for the product key.
"It tells me "the feature you are trying to use is on a CD ROM or other removable disk that is not available."
Or I get an error message saying it cannot find the required files.
Or I get various error messages in German.

It starts to configure, then asks for the disc for Office XP. Again and again and again.

I don't understand why it should have deinstalled Office XP, when I imstalled rthat seperately with a disk which had nothing to do with the pre-installed Office 2007.

I've been at this for hours now and I'm stuck.
Help!

No ideas?
Anyway, I've made a little progress. Suddenly, the invitation to enter the product key did finally appear and for the last 20 minutes or so it claims to be installing. It's maing the approproate noises. But what worries me is that there is no green bar showing in the Installation Progress window. It's as if nothing is loading. Is this normal?

Also. the little Office XP Standard for Students and Teachers windows keep popping up and telling me to insert the disk, or else it is "trying to configure". They are constantly coming and going. I'm hoping that when and if Office 2007 is installed it will go away.