1.i had created a "MULTISESSION DATA CD"(containing mp3 songs) using nero 5.the disc had a free space of 21mb since the last session.now,i decided to replace a mp3 file named "xxx".OLD(for example) with a similar file named "xxx".NEW(for example).the" xxx."new was in fact smaller in size than the "xxx".old file.logically some space on the disc has to be recovered since the new file to be written on the disc is smaller than the file existing on the disc.however,it is not possible since the disc is a cd-r and not a cd-rw. but,in this case,after the writing session was over,the space reamining on the disc was just 2mb!! how is this possible?i.e,where did the 19mb space(21-2) go away?? 2.I have burnt several cd's with multisession.now,i want to make all these small compilations into a single cd and use the old cd's for other purpose.the problem is when i burn the old cd's with new data and distribute it among my friends,the original data which is personal to me may also be accessible to them. i don't want this to happen. so,is there any way by which i can prevent others from opening or viewing the original files on the cd.but,i want the newly burnt session to be usable. may be a tweak in nero5,..? note :the cd is a cd-r burnt with iso9660 format. Before answering the question,please check out the poll!