Don't believe all you read.
Including some details is always helpful - what is, or is not, happening and system specs -
The Witcher runs fine on Win7 64bit. No compatibility setting required, but you have to install the 1.5 patch, and download and install the TAGES (copy protection) update. The 1.5 patch also allows you to play the game without the DVD.
TAGES, the AAA Copy Protection System
The game always runs at 32bit. There are very few game that have a 64bit mode, and they can also run in 32bit mode. The games that are 64bit capable need a machine with an AMD64 processor, or the most recent Intel processor (Intel has only just started producing 64bit cpus') to use the 64bit option.
If you have problems it may be your system is not up to the game (integrated graphics).