a)well, I'm afraid it's not that simple. Only a handful of drives support capacities greater than 700mb. and only a handful of readers can read them also.
I also wouldn't bother going to buy a CD-RW that supports them especially as DVD burners are becoming more affordable.
b)How much can you overburn? 2 minutes is usually a safe guess. Doesn't sound like much? Well 2 mins is 17mb so that can easily make the difference between fitting and not fitting a movie on the CD, for example.
c)
**AT YOUR OWN RISK**
Nero is best for overburning. In fact, It comes with a little utility to test the overburning capabilities of your burner/media combo.
Load (from the start menu) Ahead Nero\Nero Toolkit\Nero CD Speed.
Put a blank 700MB CD in the drive and select your burner from the bar near the top.
Then choose "overburning test" from the "Extra" menu of CD-Speed.
It should be self explanatory from there.
Once you have done that, you should have an idea of how much your media can *really* hold, or how far the drive can burn, depending on which comes first.
Then go into Nero Burning ROM and choose File --> Preferences --> Expert Features and enable overburning. You can adjust the times if you wish according to Nero CD-Speed's results, but leave a margin for error and because it varies. How big the margin should be I don't know as I just leave it on default.
Once you have put say 710MB of data into the project, go to the write dialog and make sure you have Disc-at-Once selected as your writing method.
**AT YOUR OWN RISK**