I have recently been playing Gothic 2 without expansion with no plroblems on Vista. Then I came accross the Gold edition at GOG and have installed it on XP. The framerate now drops to under 20 when I go outside. Changing the graphics settings have no effect.. I am not sure what is going on as I have a fast PC.

I have tried to install it on Vista and but explorer hangs when I run the GOG gownload. I have tried everything on the XP but it still runs poorly. As I said I have Gothic 2 (no Night of the Raven) is running great on Vista. This is the first and the last game I buy from GOG.

I'm sorry you're having problems. I have GOG's Gothic 2 Gold installed right now and everything works fine (XP SP3), so i really don't think it's fair to instantly blame GOG for the problems you're having.
You should probably send an email to support mentioning your specs and explaining your problem.
As for the installation hanging in Vista, you could try looking into Vista's UAC and/or your AV as those can sometimes cause problems during the installation process.
You could also look into the solutions for issues related to multi-core processors since you mentioned having a fast pc.
And you could always post your system specs here since that will improve your chances of getting a tip or a fix for your problem.
I have over 30 games from GOG, including Gothic and Gothic 2 Gold, and they all work flawlessy, so they must be doing something right.

When installing GOG games on Vista/7, right-click and choose "Run as administrator". This will speed things up to some degree. You can have this to happen every time by setting it on the Compatibility tab of the Properties window. Because GOG games can be quite big (2 GB in the case of Gothic II) it can take a while to initialise the download even on the fastest PCs, and this problem is made worse when admin elevation does not initialise when the file is first launched. The delay when launching very large executables is a technical limitation of Windows itself and there is not much GOG can do about it.
As for the performance problems, that's a lot harder to explain. The GOG release has the latest patches (including some GOG-specific tweaks to remove copy protection) and NotR uses a newer version of the game that is not available as a patch for the vanilla Gothic II. If you were running a lower patch with the version you have that could explain it (as could using a cracked or ripped version).
Gothic II uses its own bizarre page file handling rather than the Windows one, so for best results ensure the install folder is defragmented (many third-party programs let you defrag individual files or folders); note that some page file data is redirected to the VirtualStore location, so that should also be kept relatively optimised. This is more of a problem on XP; on Vista/7 the automatic defragging should do a reasonable job of keeping things optimised unless you are regularly adding and/or deleting many gigabytes of data at once. You may also be able to improve page file performance somewhat by installing the VDFS patch (available here); the installer won't work properly on the GOG release, but you can extract its contents manually with 7-Zip or the like. Put Vdfs32e.exe in the System directory (replacing the existing file) and run it once before launching the game again.
Other than the initialisation delay under Vista, the problems you are having are things most GOG players are not experiencing and are not an inherent issue with the GOG release itself. Unfortunately there are any number of explanations for the problems you are having, and the solutions I've listed above won't necessarily help. :(

Thanks for the informative replies guys. Most of what has been suggested are things I have done and am aware of. I still do not know why the GOG installer will not run. I run it and nothing happens for 10 mintues. Arkose you spoke of admin elevation not initialising - is there anyway of forcing it.
I generally do not have any problems installing games on this PC as it has been a reliable Vista build.
My PC:
Core 2 Duo E8400 @4000
Corsair 4GB DDR2 XMS2 PC2-6400C5 TwinX
Asus P5Q
4870 1GB
Xonar D1
Coolermaster Real Power 650w
Vista 64 & XP 32
I should add that I downloaded the GOG file in XP and then was not allowed access when I attempted to run it from Vista. I then booted XP and copied the file across to my Vista drive and ran it from there. Is there any DRM built into the GOG file that limits access.
SUCCESS
I thought I would give it one more try on Vista and this time it took about 5 minutes for admin to kick in. It installed fine even though I stupidly allowed it to install in Program Files (x86) folder. The games starts with a black screen with only the sound of the opening video playing. I can get into the main menu and start a new without any framerate issues. It makes no sense that it runs horribly on XP and just fine on Vista.
I will leave it as one of life's unexplained mysteries. Thanks again for the info and I apologize for being a bit grouchy on my first post. I am an RPG addict that needs his fix, and lets face it there are so few good RPG fixes these days.
One last thing, is it advisable installing the v1.0a English Ironkeep Community Patch ?