The 100% cpu is definately related to SQL?

When you are hitting these cpu levels run a quick query to see what's going on, get an idea of what processes within SQL could be causing the problem.

Quick example, I use this, which shows me what process is using the most CPU at the time (can be a little misleading due to long open connections). I also remove the SA login and also other logins that are part of background processes like replication.

SELECT SPID, RTRIM(STATUS), CMD, RTRIM(LOGINAME), RTRIM(HOSTNAME),* FROM MASTER..SYSPROCESSES WHERE  LOGINAME NOT LIKE 'SA%' ORDER BY CPU DESC