ok I understand than in middle of installt something went wrong and therefore grub's /boot/grub/menu.lst seems to be missing.
well since you seem to be quite newbie then
a) if it's brand new linux install maybe you reinstall it (most easiest way) or try to boot up in rescue mode .
b) or try boot up manually.
then you must know your linux root partition.
write to grub command line:
line 1:
root ([sh]hX,Y)
(s if you have it on scsi drive, h for ide drive).
x - nr of hard disk (counting from 0, primary-master=0, primary-slave=1, sec-master=2 etc...)
y - nr of partition where linux root part lies (0-...)
line 2:
kernel /boot/vmlinuz root=/dev/[hs]d[a-z]Z
again, h for ide s for scsi
a-z , well a=prim-master, b=prim-slave, c=sec-master d=sec-slave
Z = nr of partition (starting from 1)
line 3:
initrd /boot/initrd.img
this acctually depends on kernel config and might be superfluous
have fun