i have acpi modules loaded into kernel 2.6.*
but /proc/acpi/processor/CPU0/info says [ power managment: no ]
and ~/thermal_zone ~/fan are empty directories
also i don´t understand how to get my computer
into suspend or standby modes .

all the documentation about acpi tell about
installing it for the kernel and looking into /proc/acpi
but what if /proc/acpi tells that acpi is not working ?

i have amd athlon xp , and GA-7n400s-l

Well, about the power management... not all processor support power management (aka throlling) and as far as I know, AMD Athlon XP does not. Unless you are really really certain it does, forget about controlling the frequency of your processor.

Now about standby/suspend. Again, not all processor/bios supports these feature. In fact, unless you are using a laptop, your computer probably does not support these features. Then you will not be able to use the "hardware" (it's more like "bios controlled" than hardware in fact) standby or suspend mode. However, there is a "software" suspend mode that you should be able to use.
However, as this mode is pretty experimental/unpredictable, it is not in the default linux kernel, you have to patch your kernel and to recompile it. If you want to try this, search on google for "swsusp2", it shouldn't be hard to find.