This is a very wide topic and there are lots of things to consider which may be specific to each isntance. The biggest piece of advice I can offer is if in doubt go larger. Meaning things like Memory and even procesors these days are relatively inexpensive and its better to have more than not enough. But hopefully some of these can help you to get closer to the actual numbers you need. http://www.sqlmag.com/article/iscsi...nment.aspx http://sqlcat.com/top10lists/archiv...tices.aspx http://sqlcat.com/whitepapers/archi...dance.aspx
If you plan to move to 2008 you might consider compression and this should be of interest.