Onboard raid controllers

If the drives are mirrored (Raid1) the raid array can be moved to another brand RAID(1) controller (or even a IDE controller, however not as an array then); the array must probably be redefined, and the mirror must probably be rebuilt. But no data loss.
If the drives are in a RAID1 array, chances that you can move the array as-a-whole (to another brand RAID controller) without reformatting, rebuilding etc seems small in my opinion, but I have no experience on this.

However, if you change the mobo you are likely to get problems. Usually windows is having problems when you're changing the mobo. Recommended procedure: boot windows in safe modus on the old motherboard; de-install any driver which is related to the motherboard or any onboard device; move the hdd to the new mobo, boot and install drivers for the new motherboard. Still, this may prove to be difficult.

If you're upgrading from a VIA chipset to a VIA chipset it appears that the newest VIA chipset drivers are compatible with the whole range of VIA chipsets so that installing the newest drivers on the old board should suffice. Even then: you still may have problems. (for example: I upgraded from a VIA KT133 to a VIA KT400 recently. after hours of de- end re-installing drivers I ended up with a system where the keyboard wouldn't work on the new mobo in Windows, but it did work on the old mobo, and on the new mobo only in the BIOS)

The drives are configured in so called performance mode (R 0?). ie the data is spread accross both drives. My difficulty is the existing/previous mobo (MSI 865pe FIS2R) died on me so I cannot re-access the system. I have sent the board back to where I bought it, but no word after more than two weeks. As I have had so much trouble with this board anyway I was thinking of going to an Abit IS7-G but this has the silicon image controller and I really don't want to loose all my existing data. Another alternative would be an ASUS P4P800 Deluxe which has the same Promise controller. If anyone has any advice please pass it on.

Seems to me you have a problem with your supplier. MSI boards are usually quite good; what other problems did you have with them?

Now, I consider the chances of recreating the array on another brand of controller small. Not zero. You might take the chance. Maybe someone else here has the experience you need. I also consider the chances of getting problems changing the mobo as very likely. I would recommend that you:

1) tried to get an identical (MSI 865pe FIS2R) mobo, that way you'll have no driver problems;

2) upgrade to a mobo with the same chipset and raid controller;

3) find someone with a promise RAID controller, attach the array to it, save your data to CD/DVD/another large drive/..., rebuild your system on your new mobo (preferably a fresh install), restore the data.

Thanks for the advice. Seems the ASUS would match the chipset and raid controller requirements and I have had very good experience with them in the past.
Main problem with the MSI board was initially a memory incompatibility which appeared after BIOS V1.0 (Corsair 3200LL memory). This problem is documented elsewhere in the forums, but what threw me off was the configuration worked initially and the incompatibility only appeared after a BIOS update (then to V 1.2). Once this was solved I later tried to update to BIOS 1.3 using the smartupdate facility, after which the board would not post again. Had to send the board back to MSI a second time (plus charge for them to update BIOS) to get them to reflash the BIOS. They found the BIOS would not flash properly and replaced the board. This time the board failed during startup at Real Time Clock. After consulting MSI again they told me to send the board back to where I bought it originally. The vendor says he sent it immediately on to MSI but no word since. I have paid for this board at least twice when I take into account all the shipping costs and other charges etc. and I am so fed up of waiting, I am thinking of cutting my losses and going to a different mobo just to have a computer that works again. The MSI is probably a good board (they have also been reasonable when I talked with them) but ....