I've just had to replace an older SATA mobo with a newer one which doesn't have any older SATA connections (red ones). Will my older SATA drives work if I plug them in to the board's SATA 300 connections ( yellow ones ) ?

Also, the board's SATA 300 controllers are nForce . Will they deal with older Si SATA drives OK ?Yes, SATA II is backwards compatible so you shouldn't have any problems.
And the brand of the controller shouldn't matter either. (Unless you have the drives configured as a RAID array.)Thanks, deerpark. My QUESTION gets a bit complicated now.

The drives which were on the older, failed, motherboard were set to 'MIRRORED' RAID. However, the array had broken down and I was about to re-mirror it when the mobo went down. The PC was working fine on the one drive, it just wasn't running as mirrored RAID.

Now, the info on those drives is valuable to me. What should I do to ensure that I don't have to reformat when I put the drives onto the new mobo ? The OS on the drives is Windows 2000 Pro. I think the config utility for the RAID controller should allow you to build a new RAID 1 array without FORMATTING the hdd with your data.
If at all possible a backup would be a good idea though. Either backup the data you need from the drive or use imaging software to backup the whole drive.

You should reinstall windows after the move to a new motherboard. Windows doesn't like major hardware changes and it might not want to boot at all.OK, I was able to install one drive into another machine and extract all the data to an external backup drive. The second drive, however, generated the message 'Not a valide (sic) device ! ' Does that mean it's broken ? What generated that message?
How you tried formatting the drive?