5 years after the last server centric operating system from Microsoft, namely Windows Server 2003, Microsoft released Windows Server 2008 to RTM on February 4 2008. It is available for immediate download via Technet & MSDN. Windows Server 2008 is a unique & different release in many manners compared to the old server operating systems. It is loaded with features of Windows Vista & reliability of Windows Server. For the first time ever Windows Sever 2008 installation is like Windows Vista, means a big image file which reduces the installation time. However this isn't all. Windows Server 2008 Is Microsoft`s Leanest, Meanest Yet. This is first version of Server OS which can be slimmed down to even a headless configuration & you can remove everything you don't need from this server OS. The new Windows Server boasts a set of networking enhancements that dramatically boost file serving performance, and the product can be deployed in a new, stripped-down Server Core configuration, which significantly reduces the attack surface of systems hosting certain Windows Server roles. It comes with IIS 7, Microsoft Hypervisor, Windows Powershell, Headless operation in form of Server Core installation & many other management enhancements. This time installation can also be done using the newly created Windows Deployment Services which make it very easy for system admins to deploy. Windows Server 2008 ships with an overhauled TCP/IP stack and a new version of its SMB file-sharing service, which together can deliver significant performance gains in file-sharing scenarios, specifically over high-latency connections. Unlike previous versions of Windows Server, which bound network adapters to a single processor, Windows Server 2008 is able to spread the processing load for incoming network traffic across multiple processors. Another enhancement to Windows Server's TCP/IP stack is the Receive Window Auto Tuning feature, which determines the optimal amount of data to be sent over a connection at once by measuring the latency of the connection. On low-latency links, larger amounts of data can be sent efficiently at one time, but as connection latency grows, Windows Server sends less data per transmission window. Microsoft's SMB (Server Message Block) 2.0 file services protocol boosts performance over high-latency links by reducing the “chattiness†of the protocol. Rather than wait for receipt acknowledgments before sending more data, SMB 2.0 supports sending multiple SMB commands per packet. This more parallel method of operation can deliver substantial speedups that grow more dramatic as connection latency lengthens. One of the most immediately recognizable new features of Windows Server 2008 is the Server Manager, which is an outgrowth of the "configure my server" dialog that launches by default on Windows Server 2003 machines. However, rather than serve only as a starting point to configuring new roles, the new Server Manager gathers together pretty much all of the operations you'd want to conduct on your server. One of the most promising new features of Windows Server 2008 is its support for hypervisor-based virtualization. The feature, which Microsoft calls Hyper-V, enables administrators to host x86 or x86-64 operating systems on Windows Server, and compares well to VMware's ESX Server and Citrix's XenEnterprise virtualization products. One of the Terminal Services enhancements, which Microsoft calls RemoteApp, enables administrators to publish individual applications, as opposed to remote desktop sessions. I tested out RemoteApp with the Firefox Web browser, the GIMP image editing application and VMware's Virtual Infrastructure client. From a Windows XP or Windows Vista client, these applications appeared as if running locally, complete with resizable windows The modular design exhibited in Windows Server 2008's stripped-down core configuration carries over to Microsoft's Web server, IIS 7.0, which consists of more than 40 separate modules that administrators can install as needed. This modularity helps limit IIS 7.0's attack surface and keeps patching requirements as low as possible. Also noteworthy in IIS 7.0 is the server's move to XML-based text files for configuration, which can help simplify configuration tasks and broaden the sorts of tools that administrators can use to manage their configuration settings. Source eWeek
If a program runs on Vista then there is a good chance it will run on Server 2008. Most programs from what i've heard designed for XP work on Vista, so you should be fine.