Which modules get installed with modules_install

I'm trying to build a 2.6.18 kernel for XEN (level 0), and I need to make an initrd image that will utilize our HP's raid/scsi driver (cciss.o). The driver is being built and I can see it in drivers/block/cciss.o. But when I do "make modules_install", this module is not copied into the corresponding directory in /lib/modules. Why? How can I change this so that it is installed? (I do not need to know how to manually make a .ko file from a .o file.)

Thanks.

did you mead the module is not installed in /lib/modules within your filesystem within initrd.
normally it should be installed within your filesystem by make modules_install.
you can change to the source directory of cciss and type make install to force this or see any error.

Right. It's getting made but not installed. The xen compilation "build world" process is handling this.

I tried starting from scratch, but then "build world" resulted in "cannot find stdarg.h". The compilation line has --nostdinc, so I don't know WTF is going on.