1st thing
...go to "applications" and using the drop down at the top left...pop up "tools"...then "repositories" and delete them all (that can be deleted)....otherwise there will be ugly conflicts...

2nd thing
go to..

http://www.gronmayer.com/it/

go to it via the n770 browser...
pick yur poison partner...
there is a button to select all repositories...
check it ...
hit install...
and be patient....
it takes a bit to install the repos proper in the application manager...
afterwards ...going back to "applications" and using the drop down at the top left...pop up "tools"...then "repositories" again and simply disable (don't bother to delete) any repos which are dead.
That should help some...it should make a great deal more options viable.
Make sure not to exit out of lack of patience during your sojourn in the app manager...it will kick back...just let it do it's job...updating...installing etc....whatever job that may be...

Lastly...I suggest shouting "YOGURT!!!" out loud at the top of your lungs....mainly because it will shock those around you...thinking you either mad or a genius...as well it is of course therapeutic.

As far as overclocking goes...there are tweaks and power saver methods...
hum...I must admit while I use my n900, n810's and n800's everyday...all the time...it has been (sigh) a few years since I fired up my old n770....

Ach give me a bit ...I have to remember stuff I haven't thought about and used in years...