Good question, Nick.

I think you are likely to get more response if you post this question in the Vocabulary/Grammar forum.

Sometimes, it is simply a case of 'leísmo' (using 'le' instead of 'lo/la'), and it depends on the speaker. However, "creer" has different uses:

1. Creer en <algo/alguien> - Intransitive: "believe in"
2. Creer [algo/a alguien] - Transitive
3. Creer [algo] {a alguien} - Transitive

Using #2, you can say "Lo creo = Creo eso" or "Lo creo = Creo a Juan", where 'Juan' is the direct object.
Using #3, you can say "Le creo = Le creo eso (a Juan)", where the DO. is implicit, and 'Juan' is the IO.

Thanks for clarifying that for me, Lazarus. I had never been able to find a consistency to this before. As I have stated before, the problem with one learning almost exclusively from observation is that he picks up all the errors (such as this leísmo) of the native speakers.

Rocco: I realized just after posting my question that I had put it in the wrong folder. I'm actually using my mobile device for this since I don't have access to a computer right now. But thank you.

Lazarus: So, with "Le creo eso (a Jaun)" are you saying "I believe that for/of Juan"? As in, I believe that for Juans sake'

Rocco: I realized just after posting my question that I had put it in the wrong folder. I'm actually using my mobile device for this since I don't have access to a computer right now. But thank you.

Lazarus: So, with "Le creo eso (a Jaun)" are you saying "I believe that for/of Juan"? As in, I believe that for Juans sake?

I'm amazed at your talent with the mobile device. Just getting it to the right website should be good enough when doing it that way, Nick.

I can't answer for Lazarus, he'll be along later to do that.

But here's my answer to your question in the form of an example. In the context "Juan dice que va a llover hoy. Le creo eso.", we have to "add" words in English to get a complete translation. It would be something like, "I believe him on/about that," or "I believe him when he says that." That's just one of those differences in the way we say things between the two languages. More often than not, it takes more words to say something in Spanish than it does in English; this is one of those times where the English requires more words.

One of your literal translations is correct and the other one incorrect. It would be "I believe that of Juan," not "for Juan" or for Juan's sake.

I agree with hhmdirocco here.

Thank you both. I just have one more question. I also saw these examples on that site: "Le pegaron" = "They hit him," and "Le recordamos" = "We reminded him." Is that an example of a leísmo? Because I don't understand how either of those sentences could use an IOP. " We hit him"... "him" defintely seems like a DOP. Maybe I'm thinking too "Englishy".