http://www.lik-sang.com/info.php?category=252&products_id=9325 Buy that (or the Normal DS version) Put the NDS cart in the top, and the GBA cart in the bottom. Turn on the DS, and if need be, choose the DS game. Done.
You need to turn off your DS, take out the Supercard, now put in the RAM expansion, also put the Opera cartridge in the top, and turn on your DS. The opera ROM dosn't work with the supercard yet, so your just going to have to carry round two extra carts for now.
I ordered mine over the internet. Also, the Tv Tuner was annunced at the same time as the Opera browser, but no one here is interested in it as it only works with a special mobile TV signal in Japan.