.NET and NT4

I'm a newbie to .NET so bear with me....

I have a workstation with XP Pro and a NT 4.0 Server. Do I need to install anything on my NT4.0 Server to run my .NET apps? Such as the .NET Framework?

If so, is there a free version of the .NET framework only? Or am I forced to buy or download a new OS (.NET Server\BETA Version).

Thanks in advance.

Yes, you need the .Net framework. MS should have it as a free download somewhere.