It's two steps but I like to do it this way:
First create a file with a particular date/time. In this case, the file is 2008-10-01 at midnight
touch -t 0810010000 /tmp/t
Now we can find all files that are newer or older than the above file (going by file modified date. You can also use -anewer for accessed and -cnewer file status changed).
find / -newer /tmp/t
find / -not -newer /tmp/t
You could also look at files between certain dates by creating two files with touch
touch -t 0810010000 /tmp/t1
touch -t 0810011000 /tmp/t2
This will find files between the two dates & times
find / -newer /tmp/t1 -and -not -newer /tmp/t2