What do you mean by smoothly?
..Like, as in smoothly at all, or smoothly at the normal speed it's meant to run at?
Personally, i'm using a modified no$gba (get it through that 'NDSROM Player' app thing), with the update interval set at 40FPS, and the actual game speed at 150%, no frame skip - and it runs smooth as.
For comparison,
Windows 7, Build 7160
2.53ghz C2D (45nm, 6mb cache)
4gb 800mhz RAMs
ATI Radeon HD4650 512mb
Our specs aren't too far off, so you should be able to do the same.
Basically, just download the' NDSROM Player' app thing, and install it. Once installed, goto your C: drive, like this: ' C:\Program Files\NDSROM Player\Emulation ' and copy the 'no$zoomer' application, and chuck a shortcut on your desktop.
Then open up Platinum, press F11, and change the 'emulation speed, LCD Refresh' to 'Realtime*1.5, Auto'. Also, turn off the sound..
Done!
Should make it nice and smooth..
(Note: If that's still a little rough, go to options, then change the 'update interval' to 40FPS, and unselect 'Automatic Skip')
Hope that helps,
Matt.