If you don't have a backup, you can't really, about the only other way is a relatively painless Archive & Install, which gives you a new/old OS, but can preserve all your files, pics, music, settings, etc., as long as you have plenty of free disk space and no Disk corruption, and is relatively quick & painless...
Just be sure to select Preserve Users & Settings.
FWIW, you could restore all your user data to an earlier date, if you have Time Machine. But won't help you now if you don't. Why do you want to return to an earlier date? Does that mean you want to downgrade to an earlier version of 10.5, or are you missing files that have now been deleted?
If it's the latter, doing an Archive & Install won't help. But an A&I will restore the system to whatever version is on the install DVD. Might be 10.5.6 or even earlier. It will keep all your current files, as BDAqua said.
Anyway, perhaps if you explain why you want to do this, someone might be able to make a suggestion appropriate to the situation.
I was installing the files for Photoshop cs6. Something happened that my files are in different places, photoshop doesn't want to use my photos anymore because of the file they are now in, so I need to restore just from this morning before I downloaded anything. Unfortunately, I did not have Time Machine set up. Is there a way to restore settings to just earlier in the day?