left 4 dead 2 runs slow and i know i can run it?

i went to the site can i run it and my computer exceeds the recommended settings but i put all my settings on low on the game (at least i think) and it still doesn't run smoothly so i don't understand. this is my first actual computer game so i don't really know much about how it works

here are the specs

CPU

Recommended: Intel Core 2 Duo 2.4 GHz

You Have: AMD Athlon(tm) II X4 630 Processor

PASS

CPU Speed

Recommended: Intel Core 2 Duo 2.4 GHz

You Have: 2.79 GHz Performance Rated at: 5.58 GHz

PASS

RAM

Recommended: 1 GB for XP or 2GB for Vista/7

You Have: 3.7 GB

PASS

OS

Recommended: Windows® 7 / Vista / Vista64 / XP

You Have: Microsoft Windows 7 Home Premium Edition (build 7600), 64-bit

PASS

Video Card

Recommended: DirectX 9 compatible video card with Shader model 3.0. NVIDIA GeForce 7600, ATI Radeon X1600 or better

You Have: ATI display adapter (0x9710)

PASS

Features: Recommended attributes of your Video Card

Required You Have

Video RAM 128 MB 1.9 GB

Hardware T&L Yes Yes

Pixel Shader version 3.0 4.0

Vertex Shader version 3.0 4.0

Sound Card

Recommended: Yes

You Have: Realtek High Definition Audio

PASS

Free Disk Space

Recommended: At least 7.5 GB of free space

You Have: 615.5 GB

PASS