Just an idea.......... it could be that your db got corrupted, open the table that contains the date/time settings (i'm not sure of the table name on v6.34) and make sure it looks ok...
It can also be that something's wrong with the function to format the date if you have messed with the code at all...
I'm working on kind of a site news script that reads the posts in some of my forums and it also shows dic. 30, 1899 at 12:00 a.m as the date and time on all the posts on my script, i haven't had time to check it out yet but i'm sure it has something to do with the function that formats the data/time....