Compression is not simply compression. 7-zip and Microsoft use completely different algorithms to compress/decompress the files. You cannot use 7-zip to compress a file and then expect the expand.exe program to be able to decompress them. You can save some space by using Gosh's method of installation, or by removing the ability to upgrade from Win9x/Me (which I do in any case). With Gosh's method and no nLite, I was able to fit WinXP-SP2 and Office2003 (CD1) onto one CD.