Consider the following post:
Try to discover the disk size of your data for better estimates as 500 million rows with 100 columns is very different than 500 millions rows with 5 columns.
Actually, I don't know why we don't talk about number of table cells imported instead of table rows.
Without doing a complete analysis, a good start for a first SBE server (limit to 25 users) would be a 64-bit system with no less than 32 GB of memory and 8 CPU cores. The memory should be as dense as possible, from the same manufacturer and equally divided between each CPU.
Go here for more detailed QV HW tuning: http://community.qlik.com/forums/t/33509.aspx
You should leave room to increase the memory, but if the use of QlikView explodes think about using this first server for a development environment or a department with less demand and purchase a larger server based on the experience of this first server and more information about the volume of your data, the complexity of your reports and the real concurrency of the users.