OK. Read the link you posted and then ask what you want/need.

Hint: what you posted is a guide on how to compile mplayer yourself (for Intel processors).

From that I assume that you may be interested in compiling mplayer for N900 yourself (even though we have it already in the repositories).

So my answer is: go ahead and try it. You will learn a lot. And a bonus advice, I recommend you do that using gcc 4.7.2 using thumb2.

Once you manage that, "report back" (= post details here).