To fix your SKU011.CAB issue when you open excel, you can try this. If you have never edited your registry before I would back up all your work and backup your registry. To backup your registry click start, run and type 'regedit', a two pane window will open. Go into the File menu, and select Export. Find the location of where you wish to store the registry backup file, and type in a name for the file. Click on the Save button. Close the registry editor down and save the file on a memory key or any other external device.
Now to fix Excel:
1) Access the registry editor by clicking start, run and then type regedit.
2) Go to HKEY_LOCAL_MACHINE, click software, click microsoft, click Office, click 11.0 and then delivery.
3) There should only be one directory under delivery which is your DownloadCode (something like 80000309-6000-11B3-8CEE-0140047383C)
Select that directory.
4) On the right hand side of the screen, right-click on cdcache and change the value to 0.
Close down, restart and try to open Excel.
To deal with your space issues, I find the best program to clean unwanted files is Ccleaner. Its also free! Hope this helps