Since I have sufficient back up of my critical files, data recovery is not prime aim.
As you have recommended for ext3 up gradation from ReiserFS, is it possible to do it only for sda2 as the other hard drive’s FS (Sda1 & Sda3) are currently ok.
Sure, it should be no problem to reformat the sda2 partition with ext3 and restore the data to it. You don’t need to touch the system partitions on sda1 and/or sda3.
What I would be careful about though, is reusing the existing disk. Are you sure the disk is in good health (and not the trigger for this corruption issue in the first place)?
Replacing the disk, as I understand it’s just a single disk with no raid or other fancy stuff in the mix, is not that big a deal. There are good tools, Clonezilla being one of them, that let you copy over the working OS partitions to a new disk. To keep things simple, make sure the partitioning layout stays the same (sdX1 and sdX3 for the system partitions) as you probably them won’t need to have to deal with the boot configuration.
If you are sure your current disk is in good health and working other, simply reformat the sda2 partition with ext3 (either using mkfs.ext3 on the prompt, or with YaST’s partitioning utility) and restore the data needed. Change the mount point in /etc/fstab to reflect the changed filesystem.
Hope that helps,