If I was you I would uninstall the game, reboot & install again & try it with no mods until you get it sorted.
Don't install in ProgramFiles\.... & turn off your antivirus software while you install it.

Edit:
What resolution did you choose for the widescreen mod?
What is you screens native resolution?

Did you install the widescreen mod with support for multiple resolutions?

The BG1 engine is very stable you do it right.
The BG2 engine is just as buggy if you do it wrong.

Yeah, olnorton is correct: it's all about doing it right. If you install (compatible) things correctly your game (BG1 or BG2) will be stable. Something you are installing, or something you are doing is making your game unstable -- the game itself is not unstable.

The tricky part is figuring out what that is. I have eliminated everything except the widescreen mod, GUI mod, and the tweak pack. The only change the tweak pack made was to ensure I gained the maximum amount of HP when I leveled up.

I have updated my graphics drivers and my anti-virus was off during installation. I also rebooted after I uninstalled BG.
My system uses a Ge Force 250 GTS and I have Norton Internet Security for my anti-virus.
My OS is Windows 7 64-bit for my primary. I have Windows XP 32-bit available on another partition.

To my knowledge the remaining mods should be stable.

You never answered my questions on the widescreen mod.
But if you are using the TWM_GUI mod then the widescreen mod has to be set to one of the resolutions in the TWM_GUI readme.
And the widescreen mod has to be installed Without support for multiple resolutions.

Sorry about that I didn't see the edit. I set the widescreen mod for 1280 x 768. My native resolution is 1440 x 900. I did not select support for multiple resolutions.

I actually have good news. *Knock on wood* The game appears to have stabilized. After the last crash, I re-ran the widescreen mod setup twice. I have reached the Friendly Arm Inn without experiencing a single crash.

Thank you both for all your help.

It is really quite simple, and you could have saved yourself a lot of time had you taken advice given. You are still, by your description, going about it piecemeal. Here is the way to do it -- but you MUST start from a fresh install... do not skip this step, because everything must be fresh to eliminate possible errors that have crept in from previous attempts. The following may sound convoluted, but it really isn't, and it will save you time in the long run:

1. Re-install the game completely virgin. No mods, no fixes... nothing.
2. Uninstall DDrawFix (some systems don't like it, even though the latest GOG version installs it by default)
3. Play the tutorial. No crashes? Go to 4. Crashes? Post back.
4. Install DDRAWFIX
5. Play the tutorial. No crashes? Go to 6. Crashes? Uninstall DDrawFix; go to 6.
6. Install BG1UB
7. Play the tutorial. No crashes? Go to 8. Crashes? BG1UB needs close attention.
8. Install BGQE
9. Play the tutorial. No crashes? Go to 10. Crashes? BGQE needs close attention.
10. Install BG1TWEAKS
11. Play the tutorial. No crashes? Go to 12. Crashes? BG1TWeaks needs close attention.
12. Install the Widescreen mod -- read the readme!
13. Play the tutorial. No crashes? Go to 14. Crashes? You issue is with the widescreen mod.
14. Install TWM_GUI
15. Play the tutorial. No crashes? Play the game. Crashes... I doubt it by this point.

If I start experiencing crashes again I'll follow these steps to the letter. Hopefully I have seen my last game crash for awhile (knock on wood).

Thanks again for all the help Hickory.

I'm still encountering an occasional crash to desktop on BG1.

I started off with a clean install and removed the direct draw fix. I didn't encounter any crashes in the tutorial so I applied Unfinished business, the widescreen mod, and the GUI mod.

The game was perfectly stable until I tried to enter the temple east of Bergost. After the crash, I loaded the game back up and I was able to enter the temple.

Is it normal for BG1 to crash once in awhile?

Beregost is infamous for corrupting savegame files and causing crashes. Solution: always close door to Jovial Juggler in Beregost (and try to not visit Jovial Juggler unless you really need to), and never save inside Jovial Juggler. Other than that, BG1 doesn't usually crash.

The Beregost CTD problems was a TuTu problem, not a BG1 problem, and this has long since been fixed in TuTu.

If this was just a one off crash, then it's likely nothing to do with Baldur's Gate, at least directly -- it could be a hiccup with graphic drivers, or some other Windows/driver glitch. One off crashes happen in many games. The fact that you were able to re-enter the temple suggests that your save isn't corrupt, at least.

It looks like this was not a one off crash. The game CTD when I tried to enter a house in Bergost.

I have an old system lying around running Windows XP with a Ge Force 5200 FX graphics card. Would I be less likely to experience these issues on an older system?

I'm beginning to wish I hadn't tossed my Windows 98 rig last year.

You might have corrupted installation (if you didn't visit that one house yet). Try to backup your savegames and reinstall game.
Oh thanks for letting me know - I rechecked on other forums, looks to be true. I thought it was global BG bug, I remember I had some problem with savegames in BG 10 years ago at around Beregost/Nashkel. But I think all those issues were addressed with expansion which had some bugfixes.

The game, if installed correctly, is stable on Windows 7 -- you don't need XP or 98. I still say this applies, and you need to investigate and address it: