Possible Duplicate:
Is “I just spent all my money” grammatically incorrect?
“I just ate them” and “I've just eaten them” — what's the difference in American and British English?
My grammar book suggests that when using words like just you should always use present perfect.
So the correct form should be I've just arrived.
However I see a lot of I just arrived around and I wonder if this is an incorrect form but still widely used or if it's correct as well but with a subtle different meaning

alreadycomes to mind :) – happy_emi May 18 '12 at 16:59