First of all, the on-board RAID in the X48 chipset is not hardware RAID but a hybrid or "fakeRAID". I'm not familiar with the Ubuntu server distribution but since you had it installed and operating I assume it has the appropriate modules for the Intel Storage Matrix.
1) The drives, unless the partition tables have been damaged, should be individually mountable (except perhaps the failed drive). I'd recommend trying a live CD and leaving them on their "native hardware" for the initial attempt.
2) Have a look through the mdadm man pages. They have many of the tools that are used in Windows to repair and qeury such Intel RAID sets under Linux. Also run the SMART tools on the drives to check their status and look for errors and incipient problems.
3) If you can get the drive(s) mounted, either in an array or not) immediately make a backup copy of your data. Once that is done you can decide whether to try the repair/restoration as an exercise, or just blow away the partitions, and build a new array.