My question is, can I use Total Defense as a Haste partial action after I already used a full-round action? Can I use Total Defense if I am slowed (reduced to partial-action only)?
Not at all. Instead of using the extra partial action from Haste to attack or cast a spell you are using it to increase your AC. Sounds like a reasonable trade off.
Using Haste you full attack then total defence. I can see me getting out my big book of DM changes to the rules for that one.
If you don't like it, get rid of Haste, because that's the problem, not how you use Total Defense. Cal is asolutely right. If you are hasted, you can use your partial action from haste to go into Total Defense.
But on the subject of the basic function of Total Defense, wouldn't all of you think that Total Defense implies that you do nothing that would lower your defense? Basically, the way I see it, any action that could invoke an attack of opportunity, besides moving, cannot be performed. Although, maybe I'm not seeing this very clearly. I have yet to decide. It's all soooo confusing!