Is anyone willing to compile a new post with step by step instructions for us newbies?

By the way, are there any keyboard shortcuts which might help controlling N900 with the keyboard, like switching between applications, etc.?
Ctrl+backspace switches to the application screens, but it would be nice if I could choose a different application without clicking it on the touchscreen.

Also, I have found that F4 on my bluetooth keyboard brings up the application/settings menu when you're in an application (like clicking the application name on the top), F7 lowers volume and F8 increases volume.

I can do it.

Some commands need to be run as root, if you haven't already done it, install package "rootsh" and then you can gain root privileges by entering "sudo gainroot" in the X terminal.

First, you need to enable bluetooth HID support, edit /etc/bluetooth/main.conf and remove "hid" from "DisablePlugins=" line. Then send these commands:
stop bluetoothd
start bluetoothd

Now:

1. Enable bluetooth through GUI (if it's not on) and pair the keyboard with the device through GUI (although I'm not sure if pairing through GUI is necessary to get the keyboard working, but it does not hurt and you need to do it just once)
2. Issue the following command: You'll get a response like: object path "/org/bluez/11984/hci0"
4. Enter this command: hcitool scan (be sure that your bluetooth keyboard did not fall into sleep mode in the meantime and that it's still sending out information about its presence - usually indicated by blinking blue light)
After some time, you should be able to see the MAC address of your keyboard (if you don't have 10 other people having the same bluetooth keyboard in a close distance to you, you should be able to identify yours by the name)
5. Send this command: BUT you need to replace "/org/bluez/<your_ID>/hci0" by whatever response you got in step 2 (actually the ID number should be only thing that will be different) and replace 00_07_61_75_xx_xx by the mac address of your keyboard from step 4 (replacing all colons by underscores)

Now you should be able to use the keyboard, but only functional characters will be letters a-z, space, backspace and Enter (not even numbers)
To get the keyboard to be fully working, continue with these steps:

1. Download xkb-chinook.tar file from this post: http://talk.maemo.org/showpost.php?p=441444&postcount=3 and untar it to the /usr/share/X11 directory (Copy it to the /usr/share/X11 directory, then go to that directory and type "tar xf xkb-chinook.tar". You will probably have to be root to do this and you can delete xkb-chinook.tar file after you untar it to save space.)
2. Then, as root, do:
3. Type this command: hildon-im-xkbtool --list
This will list all connected HID devices, it will look like this:
The "omap_twl4030keypad" is the N900's hardware keyboard and after that line, you should see your keyboard connected (Freedom Pro Keyboard in my case above). Write down the ID of your keyboard.
4. Do: setxkbmap -device 4 -I -I/usr/share/X11/xkb-chinook -rules base -model pc105 -layout us
Replace "-device 4" with your device ID of your keyboard from step 3, if it's different, but most likely you will get 4 as well.
5. Press any key on the N900 keyboard (not on the bluetooth one). I don't know why this is needed, but it is :-)
6. Your keyboard is now fully functional.

When you turn your keyboard off and on again, it will now pair automatically and the only thing you need to do is to issue the setxkbmap command from step 4 above, to get all keys working.

Hope this helps.

JoHnY

Thanks JoHnY.

I'll look forward to trying them later.

JoHnY - think it'll likely be the fact that it only works on it's own, meaning I can't ctrl+backspace!

I wonder if it is possible to map something else to this key combo? (e.g. just ctrl on its own)

And what type of keyboard is it? Maybe someone else here does have it too and was able to get it running properly...

Ok JoHny - here goes!

I have got to this step and want to confirm that this output is correct before i go any further.

/usr/share/X11 # cp -i xkb-chinook/symbols/pc xkb/symbols/ .
cp: omitting directory 'xkb/symbols'
/usr/share/X11 # cp -i xkb-chinook/symbols/us xkb/symbols/ .
cp: omitting directory 'xkb/symbols'
/usr/share/X11 # cp -i xkb-chinook/geometry/pc xkb/geometry/ .
cp: overwrite './pc'?

you have extra spaces in these commands... Please copy it exactly