pocket pc and navigation

Right,i understand that if i get ipaq 3970 and interface it with Garmin etrax with oziexplorer and suitable cable i will be able to have running map feature with 1:250.000 topos. How many of this standard topos can i store on pocket pc ? Can you zoom on the feature on the map, like city area, and do basic navigation in the city? Are 1:100.000 and 1:50.000 topos available for the purpose of navigation street level with this set up. I would like to hear about it from someone that is using similar set up.
Cheers