I have a pentium IV with 512 MB ram and 80 GB HDD.
I first installed windows XP on the first primary partition, then Solaris on the second with 20 GB for the solaris partition, and when rebooted , the grub menu functioned as expected giving me the options to dual boot, so next I wanted to install red hat with /boot in the 3rd primary partition and / in 1st logical drive of the extended partition and swap in the 2nd logical drive. So, I went ahead and installed linux...but when I went to the disk druid partition manager, the partition manager erraneously showed the solaris partition (2nd fdisk partition) as ext3... but still I went ahead and installed linux as I mentioned above and I told to install the linux grub in the /boot partition.(3rd partition) so that it wont affect the solaris grub. But when i rebooted the system after linux installation, the solaris grub asks me the boot options(windows or solaris?) , but when I select solaris, it immediately reboots and the same rebooting process occurs each time after the grub menu comes...but when i select windows, it works fine....Why is this so...? any idea.. please..

The solution is rather simple, though not obvious.

You installed Solaris before Red Hat. So Red Hat wasn't written into the Solaris version of grub's configuration file.

You installed Red Hat with grub in the /boot partition.

So, when you boot up, you saw the Solaris grub menu, without any indidation that Red Hat is installed.

You need to edit the grub config file in Solaris to add Red Hat to that config file. Then, when you boot up you should see Red Hat as an option.

Study the grub config file in Solaris, and add an entry for Red Hat in the same format as shown in Solaris.