How should I estimate hardware requirements for SQL Server 2005 database?

We're being asked to spec out production database hardware for an ASP.NET web application that hasn't been built yet.

The specs we need to determine are:

• Database CPU
• Database I/O
• Database RAM

Here are the metrics I'm currently looking at:

• Estimated number of future hits to website - based on current IIS logs.
• Estimated worst-case peak loads to website.
• Estimated number of DB queries per page, on average.
• Number of servers in web farm that will be hitting database.
• Cache polling traffic from database (using SqlCacheDependency).
• Estimated data cache misses.
• Estimated number of daily database transactions.
• Maximum acceptable page render time.

Any other metrics we should be taking into account?

Also, once we have all those metrics in place, how do they translate into hardware requirements?

What I have been doing lately for server planning is using some free tools that HP provides, which are collectively referred to as the "server sizers". These are great tools because they figure out the optimal type of RAID to use, and the correct number of disk spindles to handle the load (very important when planning for a good DB server) and memory processor etc. I've provided the link below I hope this helps.

http://h71019.www7.hp.com/ActiveAnswers/cache/70729-0-0-225-121.html?jumpid=reg_R1002_USEN