In addition to anti-virus programs, make sure you turn off all non-essential programs (email, instant messengers, wallpaper changers, etc) before running the game.
I played Divinity at 1024x768 on a computer with 512MB memory, GeForce2 MX and a 900MHz processor (later upgraded to 1.3GHz) without slowdowns (except minor temporary ones when there were a lot of trees or NPCs on screen) or crashes (except a couple with Repair). I have DirectX 8, rather than 9, though.
You only need the latest
patch, it contains all the changes in the previous hotfixes.
Troubleshooting Tips (& manual install procedure)
