What OS are you running? Even XP supports the latest versions of DotNet.
http://www.microsoft.com/download/en/details.aspx?id=17851
Supported Operating Systems: Windows 7, Windows 7 Service Pack 1, Windows Server 2003 Service Pack 2, Windows Server 2008, Windows Server 2008 R2, Windows Server 2008 R2 SP1, Windows Vista Service Pack 1, Windows XP Service Pack 3
Unless you're trying to run this in Windows 98 or Win ME or something silly there's no reason dot net should be an issue