The rest of space is for MacOS X. There is a bug that disk utility may not calculate the partition size right. So I have to do it couple times. Although each partition is made as "free" by disk utility, later during Debian installation, they became a single big partition.
After installing MacOS X, I burned the debian base system CD and followed the installation. Most the hardware is supported except Airport Extreme card. The graphics card driver is "nv" for Xwindow. The right-button is F12, and middle is F11. I also installed laptop-net in order to switch network setting.
I have permission problems if /dos is automouted. Therefore, I change the option of FAT32 partition in /etc/fstab to be "user,rw,exec,dev,suid,noauto" and manually mount it with "mount /dos".
I tried to install GNUstep from source but failed. There are some bugs from GCC-3.4. GCC 4 is not available on Debian 3.1, therefore, I used apt-get to install gnustep-core-devel, which turned out to be very convenient. GNUstep is installed under /usr/lib/GNUstep.