I doubt there really is a perfect system and, even if there were, it all comes down to the time spent learning the program and honing your skills.
Pretty sure I could get decent results with tS4 and an old laptop...but it might take a bit longer...
If, however, you are talking about the realtime, then a 7 series Geforce or better would help (or ATi equivalent). I just put in a 9800GT and, short of extra AA settings, it runs just as good as the 7900GT it replaced, which in turn, ran just as good as the Radeon 9800 PRO before it. A decent processor (dual or quad core) and plenty of RAM help but these are all beneifts to a PC in general; not just tS7.6