Portal is nearly four years old, so most people who wanted to play probably already have. Even so, it's a nice gesture and this is the perfect time for those who haven't had the chance to play it.
Of course, you won't be able to play the game if your computer can't handle the graphics. Here are the minimum computer specifications required, as listed on the Steam website:
Minimum: 1.7 GHz Processor, 512MB RAM, DirectX® 8.1 level Graphics Card (Requires support for SSE), Windows® 7 (32/64-bit)/Vista/XP, Mouse, Keyboard, Internet Connection