HRZ, I'm not linux expert either. Here's a more detailed step for 3 & 4.

Step 3
- launch xterminal (it's already installed on N900)
- type the following and press enter
sudo gainroot
- done

Step 4
- While you are still in xterminal
- type the following and press enter
leafpad /etc/mce/mce.ini
- the leafpad application will launch. (if installed as per step 2)
- you are now seeing the contents of mce.ini file.