N800 and N810 share mostly the same hardware, so every OS running on the N810 can run on the N800, that include OS2008. Please note that OS2008 has 2 different releases called Chinook and Diablo, Diablo being the most recent one.

770 can run OS2006, OS2007HE and OS2008HE. Forget about 2006, and give it a try to OS200xHE, it is worth the effort.

Regarding the theme, I have no clue but I remember seeing it running on the 770, so you can probably able to find version for OS2007 and OS2008