Vampiric touch deals 1-6 points of damage per 2 levels, and gives you temporary hit points equal to the damage you deal.(PHB page 298) When a Duskblade channels this spell does he receive temporary hit points for all the damage he deals from the blow and the spell?
Just the spell.
Weapon damage is separate from the spell damage. You would get your spell damage's worth in temporary hit points only. Weapon damage doesn't configure into that computation. Your weapon damage happens and then right afterward your spell damage happens. Look closely at Arcane Channeling:
Arcane Channeling: Beginning at 3rd level, you can use a standard action to cast any touch spell you know and deliver the spell through your weapon with a melee attack. Casting a spell in this manner does not provoke attacks of opportunity. The spell must have a casting time of 1 standard action or less. If the melee attack is successful, the attack deals damage normally; then the effect of the spell is resolved. [emphasis: italic]