I have a backup copy of Sonic Adventure 2 in a CD-R.
What I want to do is rip the game from the CD-R, and burn it again... Though I don't know how to do this in a way that It guarantees me it'll work 100%.
The reason I need to do this is that my Sonic Adventure 2 CD-R is in a really bad state... so I want to make another copy out of it.
Can anybody help me in here? Whats the best way of making a proper image from it so I can burn it again?
Thanks!

When you burned that backup, what was the file extension of the file?

You'd do it like you'd copy any disc, though you must take into account they have multiple sessions and ISO/BIN+CUE don't support this.
You'll need to rip with Nero and spit out an NRG (Select IMAGE RECORDER from the drives box) or if you use Alcohol 120% rip to it's format (MDF+MDS I believe) or I THINK CloneCD/DVD (Who uses that POS anymore anyway) supports multisession.

It doesn't matter what the image file was before it went on the disc Devia Eleven, data is data once it's on a CD.
If the disc is in bad shape though, you may get errors in reading it when copying, in which case you need to download another copy (Mind the rules here please)

I use DiscJuggler to re-rip any worn discs. Given that most DC games were in DiscJuggler's .cdi format, then I just guessed I'd return them to that. The only formats that I ever seen for DC games were mdf/mds (Alcohol), sub, ccd (CloneCD), nrg (Nero) and cdi. Any of those programs would suffice.

Thanks for your replys
I have SONIC, NERO, DiscJuggler and Alcohol 120%...
Should I rip it with DiscJuggler like any CD? Is there anything else I need to do? Because for example, when I burned a disc the last time, I used Alcohol 120% and set it on the options to RAW/DAO and I just inserted the game to my DC and it would selfboot...
This backup CD-R of Sonic Adventure 2 is selfboot, and I'd like to keep that (I hate using boot disks LOL).
So, DiscJuggler is the way to go? I just rip it like any CD?

I don't have it installed right now to check but you just have the disc in the drive and then choose, 'Create image from...' and just select your drive. You don't need to alter any other options from there, just go ahead and rip it.