Can I get a better graphic card for the XP or do I need another pc?
If you want a better graphics card for an XP computer, you might actually consider getting a used card.
XP driver support is often better with older cards.
With new cards they focus on making drivers for currently supported operating systems.
What graphics card do you currently have in the XP computer?
And do you have enough system memory and discrete video memory for the game?
System requirements for The Raven are not terribly high for a modern game, but if your video card doesn't have discrete video memory the game may be too slow.
Getting a new PC would not be a bad idea.
Browsing the Internet with XP is risky for the average person.
You may want to keep your XP computer to play older games, but get a new one for newer games.