Windows 7 Sometimes bluescreen after startup

I kind of know what you mean but I usually find this happens before I've downloaded all the updates and hotfixes, which. usually you get through the update utility. If you want to check for yourself look here:
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I find once I've got all the available updates the occasional blue screen which you mention totally stops.
The only other thing I can suggest is to ensure everything is up to date in the driver department. That means Chipset, graphics and sound. Also run scans for spyware and virus's.
You can, rather than hunt down all the updates, install the beta version of the service pack for Vista. This contains all the updates released up to date. It will however place some text in the lower right hand corner of your desktop saying 'Evaluation copy'.
I use the beta and find Vista runs really smooth and for the most part error free. I've also got rid of the text on my desktop as that sort of thing bugs the hell out of me. Anyway if you want to use the beta go here:
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Just to mention, the best way to install any service pack is to do so after a fresh install of the os then followed by the drivers and so on. This isn't critical though so if you don't feel like doing that don't worry.
If you've downloaded the beta and want to get rid of the writing now on your destop, go to this site, use the download and follow the instructions:
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One last thing. The final release for the service pack is scheduled for early 08 with some rumours pointing to the first week in Jan', so if you can wait it'll save you some work but if your like me you'll do it just because you can....
Good luck