Wow. Not another server configuration question.
First, while AC can run on P2P quite easily, we should all agree this question is about a server and not get into a P2P vs Client/Server discussion. There are plenty on the board.
Right off, I would fire your Dell salesman if you asked him/her about 32-bit vs 64-bit, and the salesman recommended 12GB of RAM. If you use 32-bit OS, you will lose 8GB of memory as 32-bit can only use 4GB and, even then, doesn't use all of the 4GB. It is a no brainer anyway. To spend that much money for a 32-bit system puts you in the dinosaur area before you turn it on. I would definitely add another stick of RAM and get 4 X 4GBs. If you move up in SQL, not something that is easy to do now, but if you do upgrade to a SQL Server that can use unlimited memory, the more memory the better.
Are you completely set on Windows Server 2008 R2? Small Business Server makes much more sense, gives you more flexibility, e.g. RWA, SharePoint and Exchange. If you were to get the 2008 premium version, you get Windows Server 2008 Standard free anyway. But SBS 2011 Standard and Essentials is already out. So, why go with Windows Server 2008 R2 and, once again, be back in Jurassic Park, since you can get to 2011?
What do you mean by installer? Dell will build it and install the OS. Or are you talking about the network? I would go with someone inexpensive like a college student to set up the modem, router/firewall and switch along with running the cables. For setting up the overall network as far as the OS and domain, you would be better off with a MCITP. I am sure you can Google that and get a Microsoft MVP to help you.
May want to consider moving to a three year warranty as you are going to own it for at least that. Also consider adding another hard drive as a hot spare for better redundancy.
