I own the original retail game which I bought in 1999 and a Steam copy of Behind Enemy Lines (without the expansion). I can't install my retail copy because I'm on Vista 64 bit and my Steam copy seems to have major speed issues.
Now I'm interested in purchasing this game again with expansion from GOG but does it have the same speed problems as the Steam version does?
Thanks in advance.

I own both retail commandos and expansion and as far as I remember both of them worked fine under xp 32 bit - can check how they work under xp 64bit if you want me to. :)

Thanks for your reply. So you don't have any problems with speed then? I've heard a lot of people say that when they eventually manage to install it, the game runs way to fast making it almost impossible to play.

I had the speed problem you speak of with the Steam version of the game, and I'm also running Vista 64-bit.
I purchased the GOG version and after completing the first mission I am pleased to inform you there are no speed issues at all!

Use an app that slows down your CPU speed so that you can play the game normally.
I use Turbo
My CPU is 1.67 GHz. I run Turbo at 70% and the game in 1024 * xxx resolution

I've checked and I'm not experiencing any speed problems. :)