I am helping in building a server solution for a small business (20 computers).
So far the server will be equipped with a single Intel Quad Core Xeon Server 2.5 Ghz , 1333 Mhz, 12 mb Cache, 8 GB ram... a NAS will probably follow and a cabinet. The friggin cabinet costs over $1000 and is made in China...
As OS we'll probably put a licensed copy of Windows 2003 server, maybe with exchange (remains to be seen). As anti virus we're advised Kapersky business space security, duly licensed for all users... that's $400 a year in licensing fees! But it's supposedly the best.
I considered Linux for the server OS, but I think I'll go with Windows, the major reason being that last time I checked, Active directory was a bit rudimentary under Linux.
I still have to check and decide on the backup solution.
Since the business is into graphic design and publishing, they'll be storing and transferring potentially huge files.
As a last step, a network overhaul is planned.
So anyway I'm not posting all that here to brag (well... maybe just a little :-) ) but I wanted to know if anyone had any advice or comments to voice here, on that...
well... as for the cabinet and a separate NAS, that would be a waste of money.
get a high tower box with a good power supply. in addition, invest in several UPS, one dedicated for the server and another for the switches and routers.

as for the server itself, plugin 4+2 disks, 4 disks used as raid five for data , and 2 disks as raid 1 for OS.something like 4x 1.5tb disks and 2x 50gb disks. install linux + samba/appletalk/ftp and for legacy applications, install vmware to run the windows legacy applications. with 8gb of ram, you should not face any problems!

i would not use tape drives for backup as that has become old fashion and legacy. either use rsync to replicate to another server in another office. or, use an external usb disk for that. rsync will not give you a point in time copy, hence no roll back to a given version, only the latest. the usb disk can help you with that.

will linux work, yes. do you need active directory? the concept of a centralized control has started to fade.
the 20 workstations are most propably dedicated ones and users will not be roaming with their login profiles, hence i see no need for AD. even big corporates are currently looking into giving up on AD. there are other ways to centrally control systems without having to have and AD. you just need to know the tricks..
Yes AD requires maintenance and follow-up, and I also thought about giving it up. The main reason for using AD is not roaming, but access control.
The other worry I have about Linux is the drivers not being optimal for the hardware.
The list of features for the windows server also looks impressive, with things such as shadow copy file versioning - of course all things that can be set up on Linux, but not without spending an undefined time researching and testing.
Other then that, I have no problem with Linux, and naturally tend towards it, because of the control it gives me.
Thanks for you answer, btw :)
OpenLDAP is a great alternative to Active Directory on Linux. Check it out ;)
AD for access control is overkill.
What kind of access control is required?

Regarding versioning, i had one windows server installed, with all kind of features loaded, and suddently some glitch caused registry corruption. Fallback version didn't worked too (even M$ support tried to help), since it was not matching newer software installations and after fallback server failed to boot at all, so all this load of nice things just ended up in whole server reinstall and huge time losses.

Sure you can spend time installing things, but at least you will know how they work. Also there is fair solution - you get more money since you did more, or you just will pay this money to vendor for his software. If you are getting paid fixed amount, and if you save some money that required for licensing - better install Windows. Another drawback - don't overcomplicate things, especially if you are not expert in some areas, you just will loose reputation, if you will start experimenting on live customer.

I am sure also some ready made solutions available for Linux, if it is usual needs.

http://ask.slashdot.org/story/10/06/11/197220/Volume-Shadow-Copy-For-Linux
But IMHO you should use Amanda and use NAS for backups.
Tape Drives are old fashion? Are you kidding me? You can do a whole system back up on tape and buy as much tapes as you want. Go check mammoth tapes with 1.6TB in size. Other backup alternative is SAN storage which will probably kill the budget. Btw, Windows Server 2003 is now legacy. Time to update to Windows Server 2008 R2