If things are good the way they are, why are you considering the change? For the sake of change? Or are you tired of managing several user account databases? If it were me and the choice was left to me? I would have pointed the linux boxes to AD for authentication.
I've never had much luck installing the WSUS role. Your best bet is to install from the package here:
http://www.microsoft.com/en-us/download/details.aspx?id=5216
There are some software requirements you will have to meet, but you can easily download those as well.
This is most likely not...
start > run
type gpedit.msc
Computer Configuration > Windows Settings > Security Settings > Local Policies > User Rights Assignments > Backup Files and Directories
Ensure that your account has this right.
2 x 256 mb sticks pc2100 crucial ram $50.00 shipped obo.
80gb sata drive from WD $50.00 Shipped. this is new in package from newegg still haven;t opened bubble wrap.
ATI Radeon x800 Pro 256mb retail box. all items except video card and molex connectors still in package. $295.00 shipped...