I've just got this reply from Cakewalk:
"There are no problems with installing X2 on top of X1, and yes, you'll have both versions available. X2 Producer is already "expanded" and will automatically migrate any ProChannel modules you have installed for X1 Expanded. You will not need to install the Dimension Pro included with X2 as you already have Dimension v1.5 from X1. Guitar Rig has a separate uninstaller and will remain if you uninstall SONAR. Beatscape will run just fine in SONAR X2, however as it is not part of the X2 installer, you would need to reload this from X1 if desired.
If you wish to do a full clean install of everything at any point, you can follow these instructions:
To completely wipe out all of your Cakewalk programs try the following:
1) Completely un-install all Cakewalk programs from your computer. This is normally done from Start | Programs | Cakewalk. This will not remove any of your project files or audio data.
2) Next you will want to open the Run Command
a) In Windows XP this can be done by going to Start | Run
b) In Windows Vista\7 this can be done by holding down the ‘windows’ key and pressing ‘r’
3) At the prompt type regedit and click [OK].
***Backup your Registry before making edits - you do this by clicking the File menu, Export Registry File.
4) After backing up your Registry, you will want to delete the following registry keys. Delete the last folder in the chain of these keys by right-clicking on them and selecting "delete". If you do not have some of the registry keys below, it is okay simply proceed to the next one on the list. Here are the keys to look for:
HKEY_CURRENT_USER\Software\Cakewalk Music Software
HKEY_LOCAL_MACHINE\Software\Cakewalk Music Software
HKEY_LOCAL_MACHINE\Software\Wow6432Node\Cakewalk Music Software
*Please note that this will remove any effects presets and key bindings you may have made in Cakewalk. You can back these up separately if you like, using Options|Key Bindings, Tools|SONAR Plug-in Manager, and Options|Colors. Hit F1 in these views for detailed instructions on how to do this.
5) Open the 'Run' command again.
6) Copy and paste the following into the prompt:
%appdata%
7) This will open your Application Data folder, right-click on the Cakewalk folder and choose ‘Delete’.
8) Navigate to the following directories and delete their contents:
C:\Program Files\Cakewalk
C:\Program File (x86)\Cakewalk
9) Open the 'Run' command again and type msconfig Click [OK] and then click on the Startup tab at the upper right of the window that opens.
10) Uncheck all items listed, click [OK], then restart your computer. You can always recheck those items again at a later time.
11) At this point you can reinstall your Cakewalk programs."
I hope it helps.