Note... to use Action Replay cheat DB's you will need to get the AR save for your region and place it on a GC mem card in Slot B.
You can find these with google. When you get them they will have a .sav extension. You need to convert that to .gci. You can use a tool called "mdsc.exe" to convert from sav to gci.
Then use the GC save app "gcmm" to move the EUR/USA.gci from your SD to your GC mem card.
You would need a 3rd party mem card (for gcmm) with 52 block for EUR, and 30 for PAL if you get the
newest AR codes.
AR V1.14 - EUR-Latest Update 08262008 (594 Games) (52 Blocks)
AR V1.14 - US-Latest Update 08262008 (662 games) (30 blocks)
But good googling will find you ....
Combined (693 games )(227 blocks) ... this is all codes for EU/US
The Wiird/ocarina is better imho, you can make your own codes with dolphin the wii/gc emu if you get the latest svn release as it has a code searcher. You can also convert ar to wiird with some tools.
You can convert codes from/to AR/Wiird(ocarina) too....
Sorry for the vague info, but just fyi peeps
(Convert .sav TO .gci) - mdsc.exe ->
http://filetrip.net/file.php?id=8977
(Move .gci from SD TO GC mem card-b) - gcmm ->
http://wiibrew.org/wiki/GCMM
(Find cheats for Wii/GC) - dolphin ->
http://www.dolphin-emulator.com/download.html
*Guide (with DL links) for converting AR to Wiird ->
http://vggtsworld.ta-host.com/where/wiird/...ith_geckoos.htm
*Scroll near the bottom of this page
and the cmios thing...I used "miospatcher0.2" on "RVL-mios-v4.wad", so I think more versions of mios can be used, but you should use the advised v8 as Sorg mentioned.
Again, sorry for the mess of this. I "might" tidy it up...