on3st4b, i have found a solution. You MUST use xterm and vi.

1 - install (if possible) the ssh server, it be will be easier to edit the file
2 - open xterm on the n900 (or with ssh)
3 - type "cd /home/user/.config/tracker/"
4 - "cp tracker.cfg tracker.cfg.ORIG" (for make a backup file)
5 - "vi tracker.cfg" to edit the file. If you don"t know how to use vi, please read a quick tutorial on google
6 - go to the line NoWatchDirectory and add at the end of the line $HOME/MyDocs/Directory_I_dont_want_index
7 - save the file and exit
8 - "cd /home/user/.cache/tracker"
9 - "rm -f *.db"
10 - reboot the phone.

It will take some time to rebuild the index. I don't know how to purge the index without clear it

Post an other message for more help.

(if it's ok, send me my first thanks )