8.04 md raid5 troubleshooting

[Reinhard Haller]

yesterday my server sent the following fail event notice:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
[raid4] [raid10] md0 : active raid5 sda3[3](F) sdb2[1] sdc2[2] 775119872 
blocks level 5, 256k chunk, algorithm 2 [3/2] [_UU]

the output from mdadm --detail /dev/md0

/dev/md0:
         Version : 00.90
   Creation Time : Tue Nov 13 18:54:53 2007
      Raid Level : raid5
      Array Size : 775119872 (739.21 GiB 793.72 GB)
   Used Dev Size : 387559936 (369.61 GiB 396.86 GB)
    Raid Devices : 3
   Total Devices : 3
Preferred Minor : 0
     Persistence : Superblock is persistent

     Update Time : Wed Nov  9 12:16:03 2011
           State : active, degraded
  Active Devices : 2
Working Devices : 2
  Failed Devices : 1
   Spare Devices : 0

          Layout : left-symmetric
      Chunk Size : 256K

            UUID : 5eeedfbe:638b34fc:f4b4498b:51f8baf9
          Events : 0.544353

     Number   Major   Minor   RaidDevice State
        0       0        0        0      removed
        1       8       18        1      active sync   /dev/sdb2
        2       8       34        2      active sync   /dev/sdc2

        3       8        3        -      faulty spare   /dev/sda3

fdisk says about /dev/sda:

Platte /dev/sda: 400.1 GByte, 400088457216 Byte
255 Köpfe, 63 Sektoren/Spur, 48641 Zylinder
Einheiten = Zylinder von 16065 × 512 = 8225280 Bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0f8000b1

    Gerät  boot.     Anfang        Ende     Blöcke   Id  System
/dev/sda1   *           1          25      200781   83  Linux
/dev/sda2              26         392     2947927+  82  Linux Swap / Solaris
/dev/sda3             393       48641   387560092+  fd  Linux raid autodetect

The only shortly available spare device is a 1TB SATA drive.

smartctl on /dev/sda reports a healthy drive and /dev/sda1 is still available

What is the suggested way to get the array back working?
Does it make sense to "revert" the faulty state of /dev/sda?
How to partition the 1 TB drive to be able to grow the array after replacing all old drives with 1TB ones?

Thanks
Reinhard