An option could be to have generic item numbers (one item for the 'HP ProLiant DL385 G2' for example), and then update the assembly lines to match the configuration on each individual sales order (you can do this by making a drill-down into the 'Qty. to Assemble to Order' field on the sales line).
Feeding the configuration back from your website to the assembly lines in NAV would then be a customization.
Just a thought...
