Hello
i currently use RB 233 with a mini pci card based on realtek rtl8139cl and this works with no problem.
I try to use this mini pci card on rb 411 and rb 800 and this card is not seen.
Is there a support for this chipset on mips or ppc? Because i need to change these old board with newer (like rb411)
but i must continue to use this special mini pci card.

Isn't 8139 a pci 100mbps eth chip? Does RB233 really exists?

Yes the routerboard 233 exist ... it is a old model with x86 cpu.
It is a mini-pci card with realtek 8139 - like the pci but mini-pci.

RB230 is a x86 device. That miniPCI will not work on mips or other routerboards. You can try to find some other x86 device to run it on.