First thing to try is updating the firmware. I had problems installing apps when I first got my N810 but after I updated the firmware the problems went away.

If you need help with firmware updates, try this tutorial:

http://tabletschool.blogspot.com/200...-firmware.html


The second thing is, how are you trying to install these programs? Are you going to maemo.org/downloads through the browser, or are you using the Application Manager's "installable applications" section?