i wrote about this several threads down, but it's ok, i'll write it again:
acpi4linux is a work in progress - the code is not nearly complete, and there are still many features and parts of acpi that don't work yet - including the sleep states.
S0 is normal operation, so that will do nothing. S3 is suspend to RAM, which is not possible at all at the moment (but supposedly will be working in 2.6). S4 is suspend to disk, which also does not work with acpi.
the only way to get suspend in linux at the moment, ironically, is not though acpi at all, but through a completely different kernel patch. it's called swsusp (software suspend), and the page is at:http://fchabaud.free.fr/English/defa...p&FILE2=Swsusp
i honestly have never used it and can't say much more, but the install docs look pretty thorough and easy to follow. just check out the site and read some documentation.
but swsusp is not the most stable thing in the world; hard drive corruption has been reported on occasion. i'm just warning you that it's taking a risk.
(note - at the time of this post, the swsusp page was down. i don't know if it'll be back up by the time you read this - it probably will be, but if it's not, just google for swsusp or something. you may be able to find a mirror or google cache)