RAID 1 will generally give better read performance but worse write performance, so I would not use it for heavily written logs and TempDB. Ideally, you should go with RAID 10 for SQL Server when possible. See: RAID Levels and SQL Server.
As for your cluster size question, see Disk Partition Alignment Best Practices for SQL Server for an excellent discussion of all the considerations that should be taken into account. The article says it's for SQL 2008 but it is equally relevant for 2005. Here's the most important take away from the article:
There are two correlations which when
satisfied are a fundamental
precondition for optimal disk I/O
performance. The results of the
following calculations must result in
an integer value:
Partition_Offset ÷ Stripe_Unit_Size
Of the two, the first is by far the
most important for optimal
performance. The following
demonstrates a common misalignment
scenario: Given a starting partition
offset for 32,256 bytes (31.5 KB) and
stripe unit size of 65,536 bytes (64
KB), the result is 0.4921875. This is
not an integer; therefore the offset &
strip unit size are not correlated.
This is consistent with misalignment.
However, a starting partition offset
of 1,048,576 bytes (1 MB) and a stripe
unit size of 65,536 bytes produces a
result of exactly 8, an exact integer,
which is consistent with alignment.