I'd suggest downloading the latest builds of each one (and anything else you'll need such as DirectX and Microsoft's .NET Framework).
Once you install them, do a registration (online if possible as it's virtually instant) and you're good to go.
You can download the latest build by visiting the My Software page. There's also the generic Trial Downloads (all of which become non-Trial once you register them), but they don't have Vegas 6 up there anymore.
And how do I know if I need to download any additional software?
If there's anything else you need (DirectX, .NET, etc), your new computer will tell you when it tries to use it and can't find it. ;-)