Right.
To load the pre-game editor you need to be in windows. Navigate via the start menu>programs>Sports interactive and in that menu option should be "FM Editor"
then click "file>load" and it will give you a list of the default databases availiable (normally 8.0.0 and 8.0.1 if you've installed the patch"
Load the lastest database version, and then you can use the inbuilt search tool to search for whatever you wish to edit.
Once you've finished editing, save your database as something such as "personal database 1" or whatever, exit to windows, load up FM, select "start new game" and there it will ask you which database to load.
So to recap,
1.Click on the start menu in windows. make sure FM is NOT running
2.navigate programs>sports interactive>FM2008
3.load editor
4.load newest default database (
prob 8.0.1 if you've patched the game)
4.edit stuff
5.save database
6.exit editor and then load fm
7.click "start new game"
8.select database to load
9.take (your chosen team) to champions league glory or whatever