SQL Hardware Configurations

Hi everyone. I'm looking for some hardware recommendations for a SQL Server 2005 installation. I'd appreciate as much help / recommendations as possible and I'll try to give you as much information as I can. I'm happy to use HP or IBM kit.
Option 1: A SQL Server 2005 instance that can support a small / medium size business. It would be used to host a retail EPOS application and initially have 20 UK shops transmitting information to it in real time. (dont worry about the network links). The number of shops will increase to 50 within the next 2 years. The amount of storage initially should be more than enough at 500GB but the ability to add additional storage at a later time and processing power would be ideal. The SQL box will also be used for reporting by 20 users. Ideally with LTO backup device.
Option 2: Same as option 1 but a high availability cluster so that if we loose 1 SQL server the business can still function.
Can anyone please advise.
Mike.