Well, Microsoft always give the hardware requirements for the systems they sol, but everybody knows that those specs are to low, maybe they need to put in those documents “to crawl” instead “to run”.
In my experience, talking about 3 tier setup with up to 30 users, you will need for SQL server at least 64 GB RAM, I’m taking in to account snapshots, maintenance, reindexing, update statistics. the NAV server (running 2 instances, LAN/domain instance and remote with certificates instance) needs at least 32 GB of RAM and finally, the client needs at least 4 GB of RAM if you just use word, excel and outlook besides NAV client (Preferably 8).
For 2 tier setup (one server running SQL and NAV with the client running in the cliente computer) you need at least 64 GB of RAM for 30 users.
Remember , Dynamics NAV needs a lots of RAM, you can use 2.2 processors (preferably 2 procs per server) with 2 cores minimum.
The best HDD is SSD, if its to expensive, you can use SATA disks but always in RAID 10 (never use RAID 5, its very slow), you need 4 disks minimum.
Another important thing is the bandwidth, for 30 users maybe 10 Mbps for the NAV server and between NAV and SQL servers a 100 Mbps or 1 GB direct connection.
You can always enhance your NAV experience adding more memory and using less flowfields ;-).