Whoa ... let's get a couple of things out of the way first.
You have to have a burner capable of overburning. You have to have software that is capable of supporting overburning ... like everyone's fave, Nero. You then have to have cdr media that are overburnable. Some media have excess space on the ATIP which will allow for overburning information without any real trouble for the most part. Some 74 min cdrs can overburn up to 80 mins. However, some can barely overburn at all. Example: with Kodak Silver/Golds i've found that they can overburn approximately one minute more and that's about it with Nero.
So, you'll have to experiment first before knowing how much you can overburn. You would be best served by doing a simulation with Nero first before burning. If you make it all the way through without any error messages then you can probably safely overburn. If there are errors then you'll have to take it back a bit.
BTW, good for you for asking questions. You don't ask you don't learn. The only thing is that people on this board - like anywhere else - aren't too keen on people who don't utilize the search function or do a net search first to get an idea beforehand. Sure, it's easy to ask a simple question and hope that everyone jumps in and responds ... but if you ask a realllllly common question without doing homework first (like "128 or 256 megs RAM?"

then people will jump all over you.
However, you're off the hook with this one since it will take some time to learn all this info over the 'Net.