All you have to do is download the usrcheat.dat file from http://cheats.gbatemp.net extract it to the cheat folder on your acekard, if you use akaio it's in the _aio folder, then cheats Then like you said, just press start when you are on a game icon, and go down to cheats You will also need to enable cheats in the properties This is assuming that you're using the akaio firmware.
If you go to http://hp.vector.co.jp/authors/VA013928/soft_en.html and download R4CCE you can edit the cheat database files, you can add/remove games and cheats.