Developing a game from scratch (whether in Delphi, CSharp, Java etc) is going to be PITA - you have to develop first game engine (graphics part), and then make your game. This usually involves DirectX (in Windows).
There are several free game engines, where you only have to put your imagination, and not bother with "How to draw a smiley face in 3D".
Last but not least: Delphi 7 is like fifteen years old - way out of support, well behind modern software development tools. I remember in the past a teacher used to publish regular articles on Delphi, some of them were games, but I have to dig into my archives to find it.
Edit: Check delphiforfun.org, you'll find a lot of ideas there.