DarkBlizz

You could try something using cheatengine/artmoney.

I don't think Kulas Ravine is anywhere near 256, I think it's 128.

You guys remember how bloody huge the 256 maps were in SC 1?

You are playing on the wrong maps. You need 'clean' blizzard maps.

The Point Defense Drone that the Raven deploys is a pretty close replacement. Protects units...

Try playing the game with all settings on lowest and see if you still crash.

If you find after using lowest settings, your fps in game starts fine, then gets lower and lower and lower, it may be an AI issue.

Report back please.

An overheating issue;
Have speedfan running at the same time as Starcraft 2 in window mode, and monitor the temperatures. Keep an eye out for problems as you start to reach higher tempuratures, around 100*C

High settings issue or AI issue;
Try playing at the lowest possible settings. Be on the lookout for FPS drops as you get further into the game.

Update issue with AI or Launchers;
Do you remember playing Starcraft 2 just fine at a previous time? - Sandbox or lower AI versions such as 3 or 4.

As gg.sc2 said, trying another game will tell us if it's an SC2 issue or your computer's issue.

Speedfan reads heat sensors. Not all videocards have heat sensors.

Why do you say the problem is overheating? You are just saying that Starcraft crashes. Usually when a computer overheats it cuts the power to itself. Sounds like a video driver issue, perhaps.

Clear all the dust out of your computer, especially any fans. Your temperatures can drop by up to 20 degrees *C.

Download speedfan to identify where the source of the heat is coming from.

http://www.almico.com/speedfan.php

Most people know about private servers.

If you have a copy of the original Base.SC2Data (it's 709kb), use that. But like I said before, it shouldn't matter at all about Base.SC2Data, Starcraft II takes priority from TriggerLibs first before Base.SC2Data.

Is it possible to choose 'no mod' in the launcher you are using? I'm using Zoxc's, and that's possible.

Azzhair;
When did the fps problems start?
Did you have sandbox working fine?
Did you get problems when you tried a new AI?
Are there any problems on an unmodified fresh install?
40fps at menu is a bad sign. I get 150 fps in the menu, 45 fps looking at fog of war in game, and 30 fps looking at a base/action.
Perhaps it's a problem with your computer rather than starcraft 2. What graphic settings are you on? Lowest, recommended, ultra? Try lowest settings if you aren't already.

Normally when you 'install' AI, you are replacing the original Base.SC2Data with the improved AI Base.SC2Data.
Whatever launcher you use, it reads your current "Base.SC2Data" file and uses that for AI. All good.

When you extract TriggerLibs, you place it in the main SC2 directory (the one with Starcraft II.exe).
Starcraft II take priority from folders like TriggerLibs over natural files like Base.SC2Data. This is also the same for World of Warcraft.

Take a look at my post before for how to extract the TriggerLibs folder from Base.SC2Data.

I didn't say this happened to everyone.

I ran AI v6 from Base.SC2Data and my fps suffered terribly after about 5 minutes. I extracted Base.SC2data to triggerlibs and my fps got much better.

Azzhair; Are you running the AI from Base.SC2data or from a triggerlibs folder?

Quote
I keep getting "System Error. Code: 2.  The system cannot find the file specified," even when I run the launcher with no mod.  Any ideas on what could be wrong?  I've been tinkering with it for about an hour, but everything seems to be in place and haven't made any progress.

I had this problem too. Your antivirus deleted lazylauncher2.exe in the files directory of the launcher. Make an exception for lazylauncher2.exe. The launcher needs that exe to run successfully.

Download MPQ Editor (not extractor, my bad) here;
http://www.zezula.net/en/mpq/download.html

Get the appropriate version/language (you probably want 32-bit EN).

Put MPQ Editor in your Starcraft II Beta directory.
Run it.
File > Open MPQ Archive
Set "Files of Type" to "All Files (*.*)"
Locate where you put the AI Version 6 Base.SC2Data and open it
Make sure the first option is checked (internal listfile), second unchecked, third checked, fourth unchecked. Click OK.
Right-click the TriggerLibs folder in the MPQ Editor window and click "Extract".
Set it to where Starcraft 2 Beta is installed i.e. "C:\Program Files\StarCraft II Beta\"
Just for safety measures, put the original Base.SC2Data back in Mods\Liberty.
All ready.

I have the solution.

The new AI v6 lags your game really bad after about 5 minutes. To fix this, get the mpq extractor and extract triggerlibs folder from AI v6 base.s2data and put it in your main sc2 beta folder. The game runs faster from triggerlibs than from base.s2data.