Agreed, what the hell was with them calling him "Jimmy"?
... Rachel isn't too bad of a name change, I guess, but I like the name "Ran" and I also like the name "Kogoro" and it honestly bugs me when they think we need stuff "Americanized." >_> The Japanese is fine, leave it alone, it's just weird to change it.
If they were trying to pander to little kids by giving them names easier to pronounce than "Shinichi" ... I have to question how young they think their audience is. There's a bloody murder every other episode (including one where a guy carries around a chick's severed head in his shirt), Shinichi has seen Ran naked and bathed with her I'm not sure how many times, a lot of the motives are related to some pretty adult themes, every now in and then the murder was a suicide ... I dunno, but I really don't think this was intended for six year olds or anyone young enough to trip over the protagonists' names.