ok, i hope most of you all know that cd's can fit more than 700MB of raw data to a 700MB cd. its actualy closer to 800MB of space for 80min of CD audio or VCD video. The reason is that cd all have built in error protection that eliminates the need for it in the data structure of the disc. this means that all of the space can be used for useful data.
data cds, however, have no built-in error protection, and therefore cd-burning software adds it into every cd you burn. About 13% of the space on a cd is error protection, so the total space on a cd is reduced by 13% when you burn in data mode.
a few people over at the http://www.doom9.org
forums have created a program that will burn a data file in mode 2 format. In laymans terms, it allows you to fit over 700MB onto a 700MB cd.
there are drawbacks however. these cds can only be read by a system with the correct filter installed. also, since the error protection is bypassed, if the disc gets scratched near the center or the edge (where information on the file is stored, filenames, etc..) then the cd is useless. so you must be more careful than normal with these cds.
here's doom9's guide on how to do it. http://www.doom9.org/xcd.htm