d20Dwarf said:
This is only for ghost's, though. I'm talking about a different type of incorporeal creature that does not need to manifest in order to cause damage with its incorporeal touch attack.
What manifesting does for a Ghost is allow him to become incorporeal.
3.5 MM page 118
"When a ghost manifests, it partially enters the Material Plane and becomes visible but incorporeal on the Material Plane."
3.5 DMG page 295
"Incorporeal creatures are present on the same plane as the characters, and characters have some chance to affect them."
3.5 MM page 118
"When a spellcasting ghost manifests, its spells continue to affect ethereal targets and can affect targets on the Material Plane normally unless the spells rely on touch. A manifested ghost's touch spells don't work on nonethereal targets."
The implication here is that a ghost becomes an incorporeal creature when it manifests and that manifesting does not allow touch spells. A DM could rule that a Ghost attacking with an incorporeal touch attack cannot stack on its touch spells, but other incorporeal creatures can. However, I consider this to be inconsistent.
3.5 DMG page 6
"Look to any similar situation that is covered in the rulebook. Try to extrapolate from what you see presented there and apply it to the current circumstance."
3.5 DMG page 295
"Likewise, they cannot manipulate objects or exert physical force on objects. However, incorporeal creatures have a tangible presence that sometimes seems like a physical attack (such as the touch of a Spectre) against a corporeal creature."
I think that the intent is clear though. Incorporeal touch attacks are not corporeal. They are special attacks that drain life levels or do other harmful things, but they are not physical touches and hence, incorporeal creatures cannot physically touch a character in order to deliver a touch spell attack.
Granted, the clarification of this "rule" is hidden in the Ghost template, but that is not unheard of. WotC occassionally has rules hidden within spells or creature descriptions and in a later version, they pull those rules back out where they belong.