I have the same problem. 7-8 minutes to start then another 10 to open outlook express. I sat down and thought what I had changed recently. Aha! Although I had McAfee virus protection, all the other bits that come with it were previously not installed until recently. So I removed it all to start again and Hey Presto, all is up to speed again.
Only question now though is why? It is all installed on my other computer and all is fine!
Most of my mates have the answer..... they are all going MAC!!!!