He'd play either quite well.  Only problem is, he's usually a creepy scarey guy, so if he was playing Peabody, people immdediatley say "Aw, fuck.  That's John Malkovitch.  Peobody's got to be a villain."  Wonder who Gary Oldman would play best?

John Malkovich as Mac.

Jared is also way too cool looking and muscular. Harry needs sort of a geeky and vulnerable aspect to his look that Jared just doesn't have. You need to sort of believe (at least in the tv world) that Harry doesn't think of himself as much of a catch. Jared obviously spends a huge amount of time on his appearance, so I can't see him being able to believably play that aspect of the character.

And that is why Paul Blackthorne was good in the role.  Put a the hat and the duster on Paul and he's A-OK.

There's only a few roles I've ever really felt sure about.

Michael Carpenter - Ewan McGreggor http://www.imdb.com/name/nm0000191/?ref_=sr_1

I've always pictured Michael Carpenter as taller and more more substantial than Ewan McGreggor, more like Hugh Jackman.

He does have the Thomas face.  Perhaps we need further investigation on him though.  Any pictures of him, say, without a shirt on?  You know, just for comparision reasons?

He's got the eyes, though.

Remember that there's Lash, and there's Sheila.  Lash is supposed to be Greek Goddess-type.  Sheila is the 'girl-next-door' type.  Lash appears distinctly as both in DB, and after the big reveal, we never see Sheila again. 

Tilda Swinton might work as Lash.  She's not exactly what I'd pick though.  She's got the stern look for Gard, but I'm not sure what I've really seen in her in, other than Constantine.  And in that she was very androgynous, because she was supposed to be an angel.

Oops, I thought you meant Tilda as Lasciel.  Lash, Sheila?  I'm several books behind (still stuck on "Turn Coat"), due to lack of time to read these days.  I'm either getting behind on my TV shows/DVDs or on books.  Can't keep up with both due to work/eat/sleep.

I never pictured Lasciel as beautiful. 

I've always heard/pictured Harry as Mike Rowe of Dirty Jobs. I think it is the parallels between Harry getting the crap beat out of him each book, and Mike getting stuck doing the crappiest jobs every episode.
Oh and Tilda Swinton as Lash.

Those could work. 

Rasins, I don't know what a cheech Marin is. I meant that I understand the Latino part (Rodriguez= hispanic origin (I dont want to begin talking why I don't really like this usage of the word, is the current one, so it is what it is) but I don't think Latinos (or any other etnia) has a way of behave which is different than the others. That is why I didn't understand the "how is written" part, as I don't think you can tell any etnia for the behavior of a character.
Instead, I think the "half Latino" can come for the Susan part. She is not Susana, but Susan.

These days, a name means ABSOLUTELY NOTHING, first name (given name), middle name (given name) or last name (surname/family name), but especially first and middle names.  There are many examples where even the last name bears absolutely no resemblance to the person's heritage.  However, given names sometimes arise out of the whim or craziness of the parents (e.g. Moon Unit).  Rules are out the window.  Susan's parents could have just picked Susan because they liked that form of the name, or Susan could have changed it herself, for whatever reason.

Funny vid.  Not related to llamas, but just funny.  It star's a German Shepherd Dog in a suit.  You might want to turn the sound down because the guy laughs just a little too much.   

http://www.wimp.com/germanshepherd/