Get a nice i7 pc or server with a UPS, 12-16 gb RAM, a small hard disk for booting/OS and 4 hard disks for RAID 10 storage (or RAID 5 even), which the motherboard should provide directly.
Put the free version of the XEN virtualizer on it. Install some VM's you can get preconfigured from Turnkey, Bitnami or Jumpbox or make yourself. Donwload an OpenFiler VM to use as a NAS for all your file needs, including storing the VM's. One VM could have a Liferay installation for a quick intranet. Another could have Postgress or MySQL, depending on your preferences, if you need a DB.
For the employees, I agree that Macs are a good investment with low maintenance compared to Windows. Just not dealing with viruses or AV software will make your lives much easier! If you can get discounted second-hand Macs, they are a good setup. You COULD perhaps have a $1000 Mac Mini Server with all the sw you need, and use the Pages/Numbers software on the Macs instead of Office (no extra price).
As an alternative, get semi-decent clones and use Ubuntu Linux on them, they are pretty close to Windows. Make sure eveyone knows how to print to PDF, send those files to clients instead of the original non-Word files and the formatting will go through ok. Configure the PC's to store the users documents in OpenFiler. If they don't have large files (or you pay for the additional storage, like $10/user/month) and wish to be able to work from home, rather than laptops get them DropBox accounts. By the time they get home, they can open the files on their home pc's AND have offsite backup.
Don't bother with LDAP or AD. Host the company webserver at an ISP for a couple of bucks per month, as well as a mail server.
The advantage of using XEN is that you can make any additional servers needed at the office easily without messing with existing servers or buying more hardware for a while. If the hardware died it's simple to put in a new server and run the images on it, without reinstalling or even restoring from backup. Ditto if you need to move to a larger server later on or want redundancy.