Are you sure you mean a RAID? 1) Which RAID do you have? RAID1? 5? 2) What do you mean by "shows up fine"? 3) do you use the onboard raid controller or did you buy an extra raid controller? 4) did it work fine under vista/xp? 5) if you can't write to it I guess the raid is not the partition on which windows is installed. what error do you get when writing?
What I can tell you is that I run a RAID1 with 2 1TB Samsung HDDs and the Gigabyte EP45-DS3R and its working like a charm!