http://www.microsoft.com/downloads/details.aspx?FamilyId=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=enUse Google.
Phil, have you tried bugging Windows Update for the .NET framework you need?
Checked the optional updates?
Now is it .NET Framework 3.5 SP1 you're looking for? Because I think it's only labeled Vista, but also works for 7.
You must use "Turn Windows features on or off" in the Control Panel to install or configure Microsoft .NET Framework 3.5 SP1.