Patch up to 1.1 at the very least (1.2 is recommended, though), because it includes the Troll Trouble DLC and fixes a bunch of problems people were having downloading it separately. It also removes DRM--assuming you have a version other than GOG's--which makes it run faster and eliminates the need to register.
All DLC is included in 1.2, so there's no need to download any of it separately (except for the optional Polish language pack, which you can download from
here).