edit /etc/lilo.conf and remove the dos entry. Make sure also that the default is to load linux in the lilo.conf file. If no default is specified and Linux is the only entry in the file then that will work just fine. Run /sbin/lilo as root to make settings take effect.
Next, run cfdisk as root to remove the windows partition, add a new one and set the type to linux native (hex code 83). Finally run mke2fs -j /dev/hdxn where hdxn is the partition you just created. This will make it ext3.
All this as root, of course.