During the boot-up procedure, do you see a line like
        tty00 at 0x03f8 is a 16450
(where the hex value is the appropriate port address for your modem)?  If so,
I don't know what's wrogn; if not, I fixed this problem by taking someone's
suggestion and rebuilding the kernel with CONFIG_AUTO_IRQ defined (it's an
option you set during 'make config').

Good luck

        NT
-- 
     Nathan Tenny                  @
     topologist and loose cannon   @ "Sixty-four thousand, nine hundred
     svasi@cs.uoregon.edu          @  twenty-eight."
     tenny@euclid.uoregon.edu      @        -Neal Cassady