Here's modified gtkrc file for Nseries theme. It uses Droid font set and font sizes are adjusted +2.

http://193.166.155.1/~amoult/N900/gtkrc

1. Install Droid font set. Available from normal via app installer from default repositoires.
2. Copy gtkrc to /usr/share/themes/alpha/gtk-2.0 (root privileges needed)
3. Reboot or changing theme to another might be needed.