Is a true neutral character restricted by alignment from casting a spell that is, say lawful or chaotic, or can he/she cast a spell no matter if its affected by an alignment. (A lawful character can't cast a chaotic spell and a good character can't cast an evil spell, vice versa)
Only Clerics really care
Clerics cannot cast spells of an alignment opposed to their own. A TN cleric has no opposing alignment and, as a result, can cast aligned spells freely.
Casting a spell with an alignment descriptor - like [Lawful] - counts as committing an act of that alignment, no matter what you used it for. Cast enough such spells consistently and you'll see an alignment shift take place. This is true for any character, even if they cast the spells from wands or scrolls.