Isometric movement Help, please ?

Hi all, I want make an isometric game, for now I don't know what kind of, but after, I think 3 hours, to try and try I spend lots of time on forum (here) to find the solution of my problem, so, the problem is this :

I want my player move just in oblique (parallel to the white lines), and I do :D but when I press 2 arrows in the same time my cool movement go bad.

I try also with instance variable, but nothing, or maybe I wrong way, so, some ideas ?

I put some pic (this is just a test to not a game)

<img src="http://www.williamjcrow.altervista.org/file/iso.jpg" border="0" />

<img src="http://www.williamjcrow.altervista.org/file/blocks.jpg" border="0" />

Well thanks in advance

The easiest way for you to accomplish what you want would be to add conditions to your existing events to restrict the keypress to only one key, then to add 4 new events for combinations of keys with new movement angles (you might also want to change the movement amount to something lower/higher depending on the case).