Wow, a two-year-old hit game on GOG!
I've already got the original boxed release, but my version is unfortunately not Vista 64 compatible. It keeps crashing at random points mostly during combat, and at certain rather late point in the game the crashes become so frequent the game is no longer playable.
The internet tells me there is no fix for my version, but maybe the lovely people at GoG have done some patching themselves. So, how's this version? Have the 64-bit bugs been fixed?

I have the Impulse version on Vista 64. I've had the game crash on me a handful of times, but for the most part it was very playable. The impulse version is at 1.7.
You might want to try patching your boxed copy and see how it does. If you still experience frequent crashes you could try down/upgrading your video drivers.

I've tried all the usual tricks: patches, drivers, XP-mode, graphics settings etc. Lots of people have tried lots of different stuff, but as far as I know, no-one has been able to fix the problem reliably. According to the game's website, it doesn't officially support anything after XP (no idea about 64-bit XP), so I don't think they're going to release a patch anymore. Basically I've given up trying to fix my copy. That's why I was happy to see 64-bit compatibility mentioned on GoG, but I want to be sure the game works before I buy it again.
Mind you, my game was perfectly fine (well, considering) at the beginning of the campaign, crashing maybe once per evening, but it got slowly worse until I was lucky to get through 2 battles without restarting.
My crashes happen almost always in combat. Also, casting spells in item battles seems to be particularly risky for some reason. The problem gets really bad once you reach the land of the dead.

I'm actually curious as to what GOG.com's programming team does to get games to be compatible in the first place... is it as simple as making older titles large address aware, or forcing them to use a single processor core?

All I can tell you it's not the cores this time, since a program can be forced to detect and use a single core without changing the code. As far as I know, the only common thing with the crashes is the 64-bit operating system.
Anyway, I hope we get an answer from the GoG developers. I can't ask about it in support, since I haven't bought the game here.

I'm playing on Windows 7 x64 and haven't yet experienced a single crash. Not Vista, but still..

Got the boxed version running on Vista 64 a few months ago. The copy protection was expired or something. So I got one of those things so you don't have to put a dum de dum in the dee dee dee to play. Fixed that.
The patch is confusing. You have to get the right version of 1.7 for your boxed copy because there is more than one version of patch 1.7. Flog Google.
That all being done, it ran flawlessly without crashing.

Unfortunately, I can verify that the GOG version still crashes quite frequently. It happened to me almost immediately upon entering the first trial room at the start of the game, and every few minutes after that. Turning off AA seemed to help the game last about 10 minutes without a crash, but then it happened again.
I wish I had known about this issue. I feel like I wasted $10 unless it can be refunded. It's just unplayable. :(
(Windows 7 64-bit)

I've purchased a boxed version last month (the collector edition was really cheap... sorry GOG, I still prefer good old physical boxes when they are affordable). I did not experience any trouble so far, on two different computers running Win 7 64 bits with ATI 48xx graphics cards (everything maxed out, including AA). I patched the game to v1.7 before running it for the first time.
I guess your problem is not directly related to win 7 64. NVidia graphics drivers maybe, or another hardware incompatibility ? Anyway, good luck for fixing it, the game is pretty good.

I purchased the retail boxed game when it was released awhile back. Running Vista 64-Bit. No problems to report @ all. Never once did I get a crash, dropout etc. I have a ATI 4870 running the lastest drivers. It's not a 64-Bit issue, it's something on your end (i.e. drivers) Just an FYI.

I can also confirm it runs without crashing on my Vista x64 machine, both on my old nVidia 8800, and my new nVidia GTX480

That's very interesting, since I'm running Vista 64 with nVidia 8800gts. Did you experience any random crashes at all?
I tried asking the GoG developers, but unfortunately they haven't answered.

I may have had one, but can't be sure. I'm afraid I consider that par for the course with old games, and with so many saves in this game, if it did happen I wouldn't have registered it.

I do know that I played several sessions for over 6 - 8 hours straight and just enjoyed it. Frequent crashes would have stopped that.

Were you up to date with the drivers? My personal suspicion on these things is that the graphics cards are the scapegoats, and it's more sound drivers that quietly destroy things. That is just my unfounded suspicion.

Win7 x64 here and no crashes, although some bad lag from time to time. I have an nVidia 8800 GTS 512, but I forget which version of the drivers. If it matters I can look that up and post.