So you finally decided to upgrade to SQL Server 2008 but it's been awhile since you looked at options for your Raid configurations. Here's a summary of what your options are:
Raid 0 - data is spread in different disk (disk stripping) but lacks redundancy
PROS - performs well on read and write
CONS - Failure of disk means data is lost
Raid 1 - known as disk mirroring no disk stripping. Data is hosted on a single drive then copied to another drive for fault tolerance. Recommended for Transaction Logs.
PROS - Redundant so failure of a drive will not stop database access
CONS - Cost since you'll need to double the size of your disk.
Raid 5 - uses disk stripping with parity. Data is spread but also stores parity information so it can be used in case of disk failure. Best for read-based not many write operations. Also avoid for transaction log because it's primarily sequential write.
PROS - Fault Tolerance at a low price.
CONS - Write Performance. Additional time is required to compute parity info before it's written to disk.
Raid 10 - cross between Raid 0 and 1. Data is striped evenly accross all drives then mirrored.
PROS - Write performance is far superior than Raid 5 and read performance is similar to Raid 5. Offers Fault Tolerance.
CONS - Cost since you'll need twice the number of disk like Raid 1.