With Sandeep's blessing, I will tackle a server machine-- self built, probably.
However, I'm not sure you can get Microsoft's Small Business Server unless you buy the whole system, so I might just stick with Win7.
Good luck. Message me if you need help. You can buy SBS 2011 from most reputable retailers including Amazon and Newegg. In fact, if you want to get it soon, it may be your lucky day. Newegg is having a memorial day sale with SBS 2011 Essentials. It may be an exclusive deal (that's what the email says, but probably everyone got it). 25% off Essentials $400-$100=$300 for Essentials
OEM SBS 2011 Essentials:
Newegg:
http://www.newegg.com/Product/Product.aspx?Item=N82E16832416440Amazon:
http://www.amazon.com/Microsoft-Win...F8&qid=1337752478&sr=1-2-catcorrRetail SBS 2011 Essentials:
Amazon:
http://www.amazon.com/Microsoft-Small-Business-Server-Essentials/dp/B003ZWJNJOOEM vs Retail.
OEM can't be moved to a new computer unless the previous computer dies and the motherboard can't be replaced. Give MS a call and they'll give you a new key. (Lots of people just lie and say their computer died if they want to migrate. Just sayin')
Retail can be moved between computers. Only one active computer at a time. Good if you plan to virtualize one day or if you are virtualizing. Moving a virtual machine from computer to computer is much easier than moving a physical machine as you don't need the same hardware between machines.
Personally I went with OEM. By the time it comes to get a new server, I'm pretty sure I won't be bringing SBS 2011 with me. And I can't virtualize my faxboard unless I get a second server or use some trickery with Hyper-V (which would've required me to get Server 2008R2 on top).