Pixelated Box Effect, How to do it?

Question

I used virtual dub to make a video as small as possible, like 50x50 pixels. Then when I open it, of course the video is small, but good quality. I want to get a pixelating box effect, so I just opened it using full screen on my laptop then I get it. The effect is there, but not the default windows size is not. Now I was wondering if there is a method of the video opening at a 500x500 (enlarged) with the video pixelating effect which you get from manually enlarging the player window by default?
I have tried manually making it 50x50 pixels, then using WMM & Premiere to set the pixels to 500x500 so that when I open the video file it does open to the screen size I want, but the video does not turn out boxy like I want. Vd, WMM, Premiere Pro CS3 all go and "smooth" out the boxed effect for me. I am trying to recreate a scene with box effect. How to go about it?
I am not sure if I have explained it well, but there it goes
Thank you for your help

Answer 1

There is a problem with that. I have not tried mosaic, as I want the pixelation to be natural, not some kind of permanent square boxes on the footage. I will be doing an video enlargement of different pixels, having a boxed effect is not what you see in normal poor quality video.
I tried the second way, but CS3 does not allow me to enlarge it by more than 200% of the original size. a 50x50pixels will only get at best is 100x100pixels. Thats what made me move onto WMM in the first place. There is a big black frame around the video where the areas which you could not get the original footage bigger than that 200%. I have tried with different video resolutions, seems that the 200% resizing is a software limitation.
I know the idea of the limitation is I would not get any kind of "viewable" video, but thats what exactly I want. Also even though it appears pixelated during editing, after rendering, CS3 still "smooths" out the box effect for me.