You cannot use the nVdia GeForce Ti 4200 for Windows 7. That is a DirectX 8.1 video card.
Win 7 requires a DirectX 9 video card, that means you need at least a GeForce 5xxx series card (a.k.a. GeForce FX) from 2003, or a Radeon 9500 video card from 2002.
You have no choice, you must upgrade your video card if you want to use Windows 7.
You can still use Windows 7, but you will be stuck with a generic video driver until you do upgrade to a newer card. This means no Aero Glass interface (unless the GPU has the proper amount of RAM, which in your case it does not), and no gaming.