Burn'n play?
 

So what i did not understand exactly

When i buy me a gamecube.
And place a Viper GC chip in it.

Can i borrow me a Broadband adaptor, do that streaming to get an .iso on my pc, give that broadband adaptor back to my friend

burn the iso to a mini-dvd(what is better mini dvd+r oder dvd-r?)

and play my backup on the cube just with the original Viper GC chip in it??

Yes, exactly. It doesn't matter which discs you use, as long as they are good quality, but to use full size dvd's you will have to either leave the top of the case off your cube or get a new one that has room for the big discs.
AS far as +/-R goes, it doesn't seem to matter, as most of the latest bios will read both. If you have access to a broadband adaptor I would probably go for a QOOB or Ninjamod chip, as the Viper's ribbon cable is fragile, the chip is overpriced, and the other's bios can be flashed using the BBA. Other than that, the Viper is still a good chip.

oh thats nice.
so if there's anyone here who can tell me where to get such a chip in germany :)

and:
coul i then program my own games, too? like some stupid pong game *lol*
can u tell me if there is any good boards to talk about that stuf?

i know google but just type in gamecube and u won't find anything you want :/
so if you know one!

oh and that "Freeloader 1.06b" doesn't work with backup games right?

I get all my chips at divineo.com. They ship worldwide and usually have good stock. I usually get my orders in 2 days and have never had any problems with them, plus they sell replacement cases to fit full size dvd's and the special screwdriver bit needed to disassemble the cube.
There are dozens of sites out there dedicated to gamecube homebrew software now: GCdev, Team-Gx, Modthatcube,... and most have useful freeware tools needed for developingyour own software.
Sorry, I dont know about freeloader, I always do hard mods (chips).