During a recent upgrade from RH 6.2 to RH 7.2 I was asked if I wanted to perform this conversion, I said no. Can I now do the conversion now I 'm happy the upgrade worked?

yes, it's fairly straightforward, maybe a little scary tho...

to convert ext2 to 3 run

tune2fs -j /dev/hdXX

where XX is the partition number. Then you can edit the /etc/fstab file and change ext2 to ext3 for the relevant partitions. Note that you can only use this on UNMOUNTED partitions, so if you only use one main partition you will need to boot into a rescue mode or such like so as to not have your root system mounted. If you have a /usr or /home partitions you can just go down to single user mode (run 'init 1' on a console) and unmount them with 'umount /usr' for example.

You can still use ext3 as ext2, so if you don't up your fstab immeditaley it won't matter, it simply won't use the journal.

more info:
http://people.spoiled.org/jha/ext3-faq.html

"Journal" - yes I heard of that, what exactly does ext3 give you?

well ext3 = ext2 + journal. nothing more.

a journal is a maintained list of files on a partition. it's kept up to date whilst the system is running, and so if the machine crashes there's much elss need to check the disk for errors. It seems kinda strange that there hasn't always been a journal in most file systems. as checking the drives on a 10 gig partition mightn't take that long, but if your 500Gb server goes down, it could be checking for hours.

incidentally, teh journal takes around 30mb of space on a drive, so isn't worth using on very small partitions