I'm formatting and setting up the partitions in a 500GB harddrive. Its not really going to be partitioned but I believe I need to leave a certain amount for the logical part of the harddrive? what sizes are best to use in this case? i'll be running windows xp pro on it.

it does not realy matter
depending on what you want to do with your HD and depending if you are goiing to place your OS on it to
i would think a 70g C: should be more than enough and then you can have 130g for other thing and leave the rest unpartitioned for when you need and want it

okay, so 70G for the OS/logical partition, and then take a piece for what i'll need and leave some behind for later?

yes, for sound partitions 100-200g
movie partitions 100-500g
general +/-100g
and so on