As i am not very well versed in this i don't exactly know to technically explain better than giving gurus out there my requirment.
I wanted to buy a server that servers the following purpose.
Many users want to share a common location to do their work. all the users will be doing most probably autocad drawings. i need a fast system that enable users read and write files faster. what would be best solution. many users will be reading and writing at the same time.
How many users do you expect to support with this server? You have several options, depending on the answer. You could buy a NAS or PC based server, or you could build your server using FreeNAS, a Linux distro, or even W2k3 or WHS, etc.
Please clarify and I am sure the collective members of Tom's can help.
The ReadyNas Pro is a good solution for storage, no doubt. A stand alone server, can provide more capability (domain controller, e-mail server, etc) than a NAS. It is really a matter of what you want and how much you want to spend.
If it were me, until I was sure what I wanted to do, I would download and install FreeNAS on a PC with lots of disk space and use it in the interim until a solution is determined. This would cost you nothing and would provide the storage solution desired (at least in the short term).