Fully uninstall the game. Backup your savegames. Delete the installation folder. Now install the game again, you must download the new version from GOG. It should display now v1.005A.
YW.

If you are still crashing, after installing the patch, there are a couple of things to check.
Backup your save files and uninstall Divine Divinity before installing the patch. Check C:\Program Files\Gog.com\ and delete any Divine Divinity directories that the uninstall may have left in place. (Thanks Arcall, missed that step)
If you are running Vista / Win 7, you need to install by right-clicking the setup.exe and click "Run as an administrator". If you just double-click the setup.exe, Vista / Win 7 tend to block some disk writes which does not allow the game to install fully. So make sure you ran the setup.exe as an administrator. First, backup your save files if you need to reinstall.
Also, if running Vista / Win 7, right-click the game short-cut, click properties, click the Compatibility tab and check mark the "Run this program as an administrator" in the Privilege Level box. If you are not starting and running the program as an Administrator you may have problems since Vista / Win 7 limit what a program can do if this is unchecked.
If you are running Win 7, you might also try unchecking the "Run this program in compatibility mode for" check box in the Compatibility mode box. Some games run better if not in a compatibility mode on Win 7, might try unchecking it in Vista as well if all other solutions fail.
Most important, in XP, Vista or Win 7 is to have the latest video drivers installed. I had several crashes which were corrected by installing the latest driver.
Click here for ATI
Click here for Nvidia
Check to make sure you are running the game at a resolution that your video card supports. Right-click your desktop, click Properties (XP) or Personalize (Vista), Settings tab (XP) or Personalize, Display Settings (Vista) and note the resolution displayed below the resolution slider. Moving the slider to the left will show other resolutions supported by your card.
If the Configtool.exe (see attached image) does not give you an option for a screen resolution your card supports than check this thread for info on editing the Config.div file for custome resolutions. It is for a netbook but the info is valid for setting costume resolution in the config.div file on any system. Open the Config.div file with notepad.

I never had the gog version prior to this latest patch. I bought, installed and ran the game for about 4 consecutive hours without any crashes at all. Worst bug I saw was a frame animation glitch for the female warrior when facing down/left and wearing light armor.
Maybe the crashes happen in later areas. I've only ran a couple of girls (melee and mage/ranger) through the starter dungeon and down to the troll bridge south of the healers village in this version.