Firstly, lets just start by saying that everyones expectations are way too high, you think this game can run on 1280x1024 and still get 60fps, even on higher end computers. Please drop your resolution before using this, as well as other settings such as bloom and HDR lighting.

If you do not know how to turn on your console, there are a few methods, but I'll list the easy one.
1) Start up the game
2) go to "options"
3) go to "keyboard"
4) click "advanced"
5) check "turn on developers console".
after that, press the ~ key to open up your console.

commands:
mat_picmip 1 - I'm not sure what this does exactly, but I found it on the steam help site and it does improve things(you can set this to numbers below 1 as well)
mat_wateroverlaysize 8 - set to a multiple of 8, such as 32 or 64 and this does not set the actual reflection quality, just how clear the reflections are
mat_filtertextures 0 - turns off texture filtering entirely
mat_filterlightmaps 0 - turns off light filtering on walls
mat_bumpmap 0 - disables shapes in things such as water and bumpy glass

If you change all these to the settings I've given you, you should get a major boost in FPS. Let's put it this way; I went from 2 FPS on a water map made by mana (of whom I want to know how you did that) to about 24 - 40 FPS depending on what I was looking at.

If you want to just keep these settings permanent, copy and paste this into your launch options or into the shortcut you use:
+mat_picmip 0.1 +mat_filtertextures 0 +mat_filterlightmaps 0 +mat_bumpmap 0 +mat_wateroverlaysize 8

PC Specs:

Dell Dimension 3000
nVidia FX 5500 by PNY with 128mb onboard ram
1GB DDR SD RAM 333Mhz
80gb HDD (not sure of the rotation speed)
All GPHX settings low, 800x600

First off, I disagree. If your above recommended specs, you should be able to play on High settings. I don't know why some high-end machines are getting piss poor performance, and I hope for their sakes an upcoming patch fixes it because they're seriously missing out, but they shouldn't HAVE to play on low settings when they have well over the recommended settings, thats not normal. Luckily, I have had zero performance issues with the game (besides that 75% multiplayer lockup issue everyone was getting.)

mat_picmip1 turns textures to medium, this is a GREAT command to reduce loading times, and I cannot even tell the difference.

Also, probably the wrong forum to post it in, it could probably go in community tech help, or the general forum.

AMD X2 3800+ | 2GB RAM | 7600 GT | 300 GB HDD |
1024x768 High settings, mostly maxed.

well, I looked in both sections, and I didn't see any names that matched from the mod section and the tech help section. Plus, for awhile the other thread got absolutely no attention, so I just moved it here. It's sort of modding it, no?

How do i change these things back to the way they were?

Yes it boosted my fps a bit, but it isnt worth it...

Please tell me ASAP...

Oh, if you didn't set them to the launch options, simply restart your game. It isn't saved into any profiles or anything.
If you DID put them in launch options, simply go back and remove the command line.

this is what i did:

i pasted all those codes 1 on 1 and pressed enter,

got into the game and it was VERY bugged (the ground etc...)

Then i restarted the game... (so i didnt save those settings) it still was the same...

i restarted steam... wouldnt work either... then i tried restarting my comp... that didnt work too lol..

So please tell me each step... im a bit noob with this kinda stuff...

To turn off the buggy ground and stuff, turn the Mat_bumpmaps 0 back to 1.