I have this for my low level priest/mage team. (Just does renew, SW: P)

Code:
/cast [target=mouseover, help]Renew;[target=mouseover, harm]Shadow Word: Pain;[help]Renew;[harm]Shadow Word: Pain; []Renew
Same macro, broken up -
Code:
/cast - This needs no explanation.

[target=mouseover, help]Renew;  - (Allows mouse healing)

[target=mouseover, harm]Shadow Word: Pain; - (Allows Mouse attacking)

[help]Renew; - (Heals current target, if friendly)

[harm]Shadow Word: Pain; - (attacks current target, if hostile)

[]Renew - (If there is no friendly/unfriendly target/mouseover target, this will just cast renew)

As for the macro you want, try this: (Some fiddling may be required)

Code:
/cast [harm]Smite; [help]renew; [player]Power Word: Shield
If you need more character space you can try this:
/cast [harm]Smite; [help]renew; []Power Word: Shield