Okay, like the poster above said, it's good to defragment very often. In my case, I actually schedule a defragment every morning.
Second off, I'd clean up my startup entries if I were you. Almost any anti-virus program is bound to make bootup slower, and sometimes significantly. Also, don't have any spyware applications load on startup. That will dramatically increase startup time, and the shields aren't that great anyhow, IMO. If you do want the shields though, boot it up yourself after Windows starts.