How do I get my system to hibernate? I don't even know what programs or modules I'd need.
I'm running slackware 10.0, and the computer I want to hibernate is NOT a laptop, it's a desktop system.

Oh yeah, I forgot: running kernel 2.6.9
I know that apm used to take care of this, I think now it's apci or something? anyway, I found a control panel in KDE but I can't access most of the settings because it says apci was not completely installed. but these options are for battery-related stuff, which I doesn't apply since I'm not on a laptop.
anyone know how to make a desktop hibernate?

You can use swap-suspend (aka swsusp). It is working well in most cases, but it is not trivial, and you can loose data if you don't know what you're doing.

Yves.

There doesn't seem to be any swsusp executable on my system, but I think I found it as a module:
$ locate swsusp
warning: locate: warning: database /var/lib/slocate/slocate.db' is more than 8days old
/usr/src/linux-2.6.9/arch/i386/power/swsusp.S
/usr/src/linux-2.6.9/Documentation/power/swsusp.txt
/usr/src/linux-2.6.9/kernel/power/swsusp.c

now how do i configure it to use it? and how serious is this data loss? are there alternatives for desktop hibernation?

From what your locate says, it seems that the module in not compiled into your kernel. You'll find proper documentation here:
http://softwaresuspend.berlios.de/

As for data loss, here's the risk:
- you hibernate; the PC halts while things are still opened/running/...
- you restart the PC without resuming the hibernated session;
- you halt the PC;
- you resume the old hibernated session.
With this scenario, the resumed hibernated session will have pointers on false data and processes, and more generally places on disk, because the previous normal restart of the PC has fsck'ed the disks, and changed things, of course. If nothing else, then at least log files have changed, and some home-directory files.
Result: uncurable fast aging of the filesystem; in a matter of hours, you won't be able to read existing files, write new files, or even change directory. Because the one time the PC was not in sync with the disks, uncurable and fast-expanding damage was done to the filesystem (not the disk itself). Only solution: reformat, reinstall.

Conclusions:
- While this scenario seems unbelievable, it is not, because it is easy to choose the wrong line in the boot menu, especially when there are several users (I know, it happened to me); and the swsusp script may not be perfect on first try. So you have to secure the boot process, and make sure all is working OK (some services and modules should be stopped/unloaded before suspending, and restarted/reloaded on resume).
And be sure TO BACKUP YOUR DATA before trying anything.

I hope I have you affraid No, just be carefull. I had swsusp working OK on my PC.

Yves.