ACPI is bogus in my opinion. It never works for me either.... I have a dell too. Use APM. It's as easy as could be.
cd /usr/src/linux
make menuconfig
get into the Power Management section. Completely uncheck the "ACPI" and check APM. then scroll down in the heading and check "enable PM at boot time". I always integrate those into the kernel vs. Modules... Keep backing out until it asks you for the final save.
make clean bzImage modules modules_install
I always delete everything in /lib/modules/2.4.22 before I do that. I'm sure it's completely unnecessary. I never have 2 options in grub any way so I don't want left over modules laying around. Doing this type of minor tweaking to the kernel won't result in a non-compilable kernel anyway. Up to you. If your going to go crazy and douche the kernel, don't delete anything.... Keep the old kernel and modules around and make a new entry in your bootloader. Otherwise,
Delete
/boot/vmlinux
/boot/vmlinuz-ide-2.4.22 (or whatever it is)
/boot/System.map
(If you use grub, delete everything in /boot except for /boot/grub)
Cut
/usr/src/linux/System.map
/usr/src/linux/vmlinux
/usr/src/linux/arch/i386/boot/bzImage
into
/boot
modify grub or lilo to reflect the changes. bzImage is what you want the bootloader to point to.
Not sure why I just posted all that when there is an awsome guide already here.....
Sorry....
Jon