Let's see...here's how to do things:
1. get both the latest postloader and the latest plugin package from
this site (as of writing, it's 4.0.5 and plugin pack 3).
2. install postloader as described in the .zip file. The content of the plugins..zip file go in your \ploader folder. So on SD, it would look SD:\ploader\plugins.conf, SD:\ploader\plugins\fceugx.dol, and so on.
3. open the \ploader\plugins.conf file with notepad. After the rom is the directory where postloader expects you to place your roms (this is pretty much standard: genesis roms go in /genplus/roms and N64 ones go in /wii64/roms, to name a few)
4. start postloader.
5. press the 'down button while pointing the wiimote to your screen (or select the emu-thingy from the list).
6. it should display your roms now. If needed, you can set up some filters with the '2'-button (e.g. if you only want to see N64 games).
7. start whatever game you want by doubleclicking on it.