E7200 Processor@ 2.53GHz
4GB RAM and 250GB HDD
There is a "What Do I Buy" section on the forum, that is where your question belongs. Vista is the current Microsoft Operating System. Some systems can still be ordered with XP and some can only be ordered with Vista. Windows 7 will not be available until (last I saw) the 1st of the year, so you can't order a new PC with Windows 7. The server version you reference is not for a desktop system.
Basically, you are down to Vista or Windows XP, if it's available. Microsoft is not supporting any more "fixes" in XP but they will be supporting security updates for a couple of more years.
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Dell forum member since 2002
Dell Inspiron 15 - 5577 Laptop
Home Built Desktop PC with ASUS ROG Z170, i7 6700K CPU
Windows 10 64 bit Pro and Windows 10 Insider Program Beta Versions. SSD drives. Cakewalk by BandLab and Studio One 4.1 Recordng Studio Software.
Dell S2719dgf Monitor
Member of Nashville based R.O.P.E.