First option*:
There's a nifty little program called NDS2xGL that you can try out, check it out here:
http://www.emutalk.net/showthread.php?t=40465
In order to use the program, though, you need to have your GBA Mode to 'VGA (poppy bright).' If you don't like that mode, then wait for a new version, or...
Second option:
...play NO$GBA in 640x480 resolution by changing the program compatibility or your whole computer's resolution. I recommend changing the program's compatibility so you won't have to keep changing your computer settings.
To change the resolution NO$GBA runs in:
01. Right-click the NO$GBA icon > Properties
02. Go to the Compatibility tab
03. Under 'Display Settings,' check 'Run in 640 x 480 screen resolution.'
04. Apply your settings and click OK.
Hopefully this helps! It's been said that this may also increase speed a little bit, but I don't know if that's true.
* Download link offered in link doesn't work. Download NDS2xGL here (the .rar includes the whole NO$GBA directory with the plugin); thanks Dung for the notice!
ps. Sorry if this has been posted already, or if I'm posting in the wrong section. I'm new.. hey everyone!