Install with custom kernel

I need a custom-built kernel to see the hardware on my machine.
My hardware is not supported by stock kernel.

I compiled the kernel I need on another machine and I know it works because I have an identical machine which came wit some Linux preinstalled and I was able to add my kernel to the boot menu.

What I did is:
1) cross compile my custom kernel
2) copy over bzImage and the modules directory
3) adjust accordingly /boot/extlinux/extlinux.conf

and it works ok.

Now I want to install ubuntu on an identical hardware.
I did some testing:
1) I need to boot from SD/MMC card
2) I downloaded ubuntu-11.04-alternate-amd64.iso
3) I transferred it to SD using unetbootin
4) my machine boots from SD and displays UNetbootin menu
5) keyboard works here because it is still using BIOS
6) selecting any (useful) menu entry boots stock kernel and displays "Ubuntu installer main menu"
7) I cannot interact anymore with my machine because keyboard is unavailable.
8) actually most peripherals, including USB and disk are not available any more!

Do You have any idea on how should I proceed?
I will presently try to patch directly the SD card, but I do not expect it to work.

Thanks in Advance
ZioNemo