Do you have a EU HD2, or a TMOUS one? The European ones have far less ROM space. You could try a smaller system partition by modifying the flash.cfg file in the folder which you flash CWM from, just do a nandroid backup in CWM first, then restore it into your new smaller system partition after re-flashing CWM with the smaller system partition. I wouldn't go any smaller than 150 mb for a non-Sense ROM, if you go too small then your ROM won't boot up, or will have too little room to run comfortably. But too large a system partition will just waste internal storage space.
But if all your apps are getting installed to your partition by default, 200+ mb is more than enough internal storage for your phone to run nice and smooth. But that's also why I recommend DT's A2SD script, because not only does it move all your apps to the partition, but your dalvik-cache too (anywhere from 30-75 mb) and with the A2SD GUI app, it's easy to do more to make your phone run smooth, like enabling zipalign at bootup.