pcmcia config defines ide_cs whereas the kernel module's name is ide-cs. this is actually documented in README-2.4 for pcmcia-cs, where they recommend to change all instances of ide_cs to ide-cs in /etc/pcmcia/config Perhaps gentoo ebuild scripts could do this automatically if running under 2.4 kernel.
Fixed in pcmcia-cs-3.1.34-r6 (which is currently masked because of the segfault prob in cardmgr when run with the -f flag, however I haven't been able to reproduce that error)