I compiled a kernel,
and when I boot I get this message:

VFS: cannot open root device "hda2" or unknown-block(0,0)
Please append a correct "root=" boot option
kernel panic: VFS: unable to mount root to uknown bock(0,0)

I'm using grub, and heres my grub file:

title Debian GNU/Linux, kernel 2.6.6-20041214
root (hd0,1)
kernel /boot/vmlinuz-2.6.6-20041214 root=/dev/hda2 ro
savedefault
boot

title Debian GNU/Linux, kernel 2.6.6-20041214 (recovery mode)
root (hd0,1)
kernel /boot/vmlinuz-2.6.6-20041214 root=/dev/hda2 ro single
savedefault
boot

title Debian GNU/Linux, kernel 2.4.27-1-386
root (hd0,1)
kernel /boot/vmlinuz-2.4.27-1-386 root=/dev/hda2 ro
initrd /boot/initrd.img-2.4.27-1-386
savedefault
boot

title Debian GNU/Linux, kernel 2.4.27-1-386 (recovery mode)
root (hd0,1)
kernel /boot/vmlinuz-2.4.27-1-386 root=/dev/hda2 ro single
initrd /boot/initrd.img-2.4.27-1-386
savedefault
boot

Now the fitst two don't work, but the last 2 work.
Any ideas?

How much information do you get from the boot sequence prior to that error? Do you at least get processor detection and stuff like that, or does it come up with that error immediately?

If you are getting processor detection and stuff, the first thing I would start looking for is at your kernel configuration to ensure that you have your IDE controller built into the kernel. If the system doesn't know what to do with your IDE controller, it can't detect the drive and thus cannot boot from it (the rest of the way)