Hello –
I’m reasonably new to this industry but i have done a couple HD projects and as far as I understand the only difference between HD and SD is pixel dimensions – whereas typically you might work in a 720×486 (D1) workspace – HD comes in 2 formats – 720p (1280×720) and 1080i (1920×1080) – these are actually presets in your comp setup window, so yes you can do HD graphics – the only difference is greater render times –
Hope this helps,
Travis