Unless you are designing a replacement for the Space Shuttle, the 100% spin is related to poorly designed queries/sprocs, missing & deteriorated indexing.
Easiest to detect: SQL Profiler duration > 3000 batches, t-sql . (You can start higher and proceed lower)
Look for READS HOGS. Ignore the low reads sprocs which were blocked.
Generally if a sproc is doing over 5000 reads, it is a target for optimization. Exception are infrequently executed batch jobs.
Start with reindexing all your tables with 70% fill factor ( static tables 90%).
SQL Server 2005 Performance Tuning - http://www.sqlusa.com/order2005highperformance