OS questions...

Windows 7 Home Premium 64 bit will only support 16 GB of memory, Professional supports 192 GB, but finding a motherboard that will support more than 32 GB is pretty tough/impossible. The 32 bit versions of either one will be limited to a 4 GB (not all of it available to programs). There are a number of other features on the professional version, but they will not affect how your DAW runs.
 
http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx
 
http://windows.microsoft.com/en-us/windows7/products/compare
 
The general purpose OEM versions are supposed to be identical to the full retail version except for the license.  If MS enforces that license, you will not be permitted to move your OEM Windows to a new machine--it is locked to the machine which it is activated on the first time. A new machine need not be an entirely new box--replacing your motherboard would probably be treated as a new machine. Other changes to the machine that would trigger a requirement for re-activation would probably be granted re-activation with a telephone call, but who knows. You should have no trouble upgrading from an OEM Windows 7 to Windows 8 using an Upgrade version of W8 on the same machine. Microsoft will not provide support (technical assistance from a Microsoft "engineer") for an OEM version, but you can get updates, bug fixes etc. directly from Windows Update, and do your own self-support using the knowledge base etc.
 
Beware OEM versions that are re-sales of vendor-specific versions of the OS that sometimes find their way into the grey market. I got one for an earlier version of Windows years ago that was linked to a vendor's brand name machine and would not install on any other machines. These are usually the discs that ship with the machine for use if the hard drive crashes; they may be described as "installation" as opposed to "restore" discs, but they are printed by or specifically for the computer maker.  The larger more respected computer parts sellers will not carry these vendor versions, but some of the really super deals from unknown sites or garage sales may be bogus.

The professional version has networking security features that home does not have.  My wifes office bought her a IBM Thinkpad laptop and it was critical to have professional installed so she can remote  the office server securely. 

The OME  OS stashed in a partition is a danger to many people who never take the time to burn the disks. In my case I have a netbook and there is actully no Disk drive! So I have never backed up the OS.
I'm not worried as it is only XP so no loss. I beleieve you can download from the ASUS site too...hmm, I see the MS label on the botton is unreadable now! 
 I should probably swap out the hard drive soon as this one is 3 years old. I'll go with W7 next time anyhow.

The other bummer with OME OS is the disks often are Bloated with crap you do not need. My mother in laws Acer was just a bunch of total junk that took an hour to delete after I re did it.
So there is a benifit in having a proper MS OS full install on a disk in your posession.
I'm not sure about windows 7 but XP pro used to allow 2 computers to share, I still have that version.

syntheticpop


What will Windows Professional do for my DAW build vs. using Windows Home Premium? If I use the OEM version, will I be able to upgrade it to the next version? And what are the limitations? If there are any using an OEM install.

ram already addressed. as well as networking features you dont need.
 
OEM(not from a box slinger (EG Dell etc)): can be put on any computer you want no need to worry about upgrades but yes you can.
generally an OEM full version is less than an upgrade anyway so a moot point.
 
you can move OEM from computer to computer as long as its removed from the old. (MS has a new thing now anyway that shuts off more than 1 running system with the same license anyway) and you were not goofy enough to stick the COA to the case.
 
OEM can be leagally purchased with any hardware sale. (EG a mouse, a HDD)
not supposed to be sold by itself.
 
OEMs sold that came from a box builder is highly illeagal. had a local company around here that did that like 8 yrs ago. $500,000 fine plus criminal record..
 
 

I was hoping I could set the whole family up with professional from the one OEM version. Haven't gotten around to learning how.

 
 
You could certaininly install the system from the same disc on multiple computers, but you will have trouble activating it on more than one. The discs for a given version of windows are all identical, so one disc works for unlimited installations. The identity of the particular copy you are licensing/activating is the printed alphabetic code included with the packaging. In order to activate additional installations you will need additional activation codes for each machine it is installed on. You would probably have better luck getting a cracked version that does not require activation from a pirate distributor than using a legitimatly printed CD to try to get MS to activate it on multiple machines.
 
The cheap and legitimate way to economize on multiple Win 7 was the Family Pack, which gave you three licenses (3 activations) from the same code. That may still be available, and cost less than two full OEM copies, but as far as I know was never available for the Professional version, only Home Premium.

M$ got smart starting with Vista.

if you install (OEM or retail) on mulitple systems using the same COA (license#) it will disable the first system
unlike XP you can not use the code on 2 systems. now if you never connect the system to the internet you think hey i am good,

wrong it times out without an authentication code,
on the other hand if you NEVER click the register now button you can pull it off for a period of time.

just no way aroung having to buy a copy for each system. and rightly so.

moving it from one system to another (with the previous begin decommisioned) is a different story.