Poorly configured and under-sized I/O subsystems are a very common problem with SQL Server 2005. I think that this often happens because SQL Server 2005 is so easy to use that many inexperienced DBAs or non-DBA type people can get a server and database up and running without really knowing what they are doing.
It is very easy to right-click in SQL Server Management Studio (SSMS), and create a new database with both the data and log file on the C: drive of a server, (which is a formula for disaster). By default, a SQL Server 2005 instance will have only one TempDB data file, again on the C: drive.
It is also very common for non-DBA, IT people to spec-out a DB server with lots of RAM and multiple, multi-core CPUs, but only a few internal drives, leading to very poor I/O performance.
No one has ever complained about an application or DB server being "too fast", and I think it is false economy to try to scrimp on your DB Server hardware. It is even worse to not properly configure the hardware that you have to get the best performance that you can out of it.