If you have used Multiboot and ever tried to install U-Boot with it you should have noticed some warnings that Application conflicts with another application install. well that application is Multiboot. You can't run both at the same time. but at TMO Melisa Queen posted a guide for this to install U-boot with Multiboot and then boot Nemo with it. Here is the Guide:
But first a small warning IF ANYTHING GOES WRONG THEN IM NOT RESPONSIBLE. DO IT AT YOUR OWN RISK.
Here is the guide for creating a .item file for mulitboot to load U-Boot:
Open Xterminal and type:
Note that leafpad and wget should be install. if not installed in your N900 then install them by open Xterm and type apt-get install leafpad wget