OK...here goes...Install the Night Skin first (as it's the skin I use and can therefore say precisely where to go, you'll have to find the equivalent options in your own skin, though the playlist we create should still be available) -
http://forum.xbmc.org/showthread.php?tid=133768
Step 1 - Getting the media in the correct place
You'll need to have something like
C:\Movies\
C:\Skate\
C:\Documentaries\
I'll refer to them like this throughout, you can just substitute the paths you are using
Step 2 - Creating playlists
On the main menu go to Videos, Movies or TV Shows - go to the submenu and choose Files
Hit Backspace
Choose Playlists
*****
Choose "New Smart Playlist"
Type = Movies
Name = Movies
"Add" a rule and choose (Paths) - (contains) - C:\Movies
"OK" and save it
*****
DO the same thing again for "Skate", and again for "Documentaries"
Step 3 - Adding them to the homescreen
Go to Settings --> Skin --> Custom Home
Go to Custom Playlist 1 and hit Enter
Choose "Set Label" and enter "Movies"
Choose "Set Playlist" and choose Movies.xsp (this is the playlist we created in Step 2)
Go to Custom Playlist 2 and hit Enter
Choose "Set Label" and enter "Skate"
Choose "Set Playlist" and choose Skate.xsp (this is the playlist we created in Step 2)
Go to Custom Playlist 3 and hit Enter
Choose "Set Label" and enter "Documentaries"
Choose "Set Playlist" and choose Documentaries.xsp (this is the playlist we created in Step 2)
Step 4 - Getting rid of the original "Movies" option that would show everything together
Go to Settings --> Skin --> Home Window
Select which Menu Items you would like to hide (Definitely choose to hide Movies as this is the one that would show EVERYTHING all together)
I personally hide Videos, Movies, HD Movies, Pictures, Favourites, Weather, Shutdown
My homescreen shows Music, TV Shows, Films, 3D Films, Comedy, Sport, Addons, Settings (Films, 3D Films, Comedy and Sport are all playlists I created as described)
Let me know if you need any more help. If you struggle to get it to work with your chosen skin, let me know which skin you are using and I'll see what I can do.