With a small installation of less than 10 users, the server does not need to be particularly powerful. A single processor machine with Windows 2003 server would suffice (although FileMaker Server Advanced can be hosted on a Windows Vista Business machine). FileMaker can also be hosted on a Mac computer. I would recommend 4Gb RAM, although 2 GB would actually suffice. The more memory you have, the better the performance.
For redundancy and data protection, I would recommend using RAID 1, although again, we have customers who are not using RAID. Personally I would always use at least RAID 1, if this data is important to the operation of your company! Performance of the database is always improved by having a fast disk sub-system. Given the choice, I would choose SCSI technology, but that is more expensive than the more common SATA technology.
Database Backup, especially to a different physical volume is extremely important. FileMaker Server has an excellent backup facility built in and we recommend at least two backups per day. More if there are many transactions.
If the server does go down, FileMaker can be easily hosted on a temporary basis using the standard FileMaker Client, but it’s not recommended to do this long term, only whilst the server is recovered.