Inland beat me to it.
You could get either the HD3850 or the HD3650.
I have no idea why the people at Circuit City thought the HD2400 would "fry your motherboard," but I wouldn't recommend the HD2400 for the games you want to play. Check what's available at Newegg.com

Thank you all,

I'll try to get the HD3850 or the HD3650 that you recommend. I know I need a new computer, I have been delaying it because of a couple things - price for the top of the line, Vista that doesn't seem to be very good and the uncertainty with motherboards with DDR2 and DDR3, I like to buy these computers to last long time and be fully upgradeable.

Today, Friday, I ordered the ATI HD-3850, I let you know the result after I install it.

I received and installed the card, the game has started.

Here I am again!

The game played with great graphics in the Normady and Citadel, but on the surface of Therum, those black patches appeared, the biggest problem is that I drive blindly on those patches and fall in the lava, I progressed inch by inch saving constantly to the refinery, there I had good graphics again but when I left the same problem, at this time the problem is even worse because the game doesn't allow saves for a long long stretch, I tried to get a code to make Mako invincible or that would allow me to save even when in combat, that I am not even in combat for long distances, I found every kind of codes but no those.
I have tried changing the video settings, everything looks bad and doesn't solve the black parts. I have 3 G RAM and a recommended sound card. Any ideas?

Have you tried changing your video drivers?

Yes Jenny, I have the latest ATI, and I installed it again in case it was corrupted.

This problem only appears on the terrain, anywhere else the graphics are great and running very smoothly, no jumps or bad texture. I can see enemies and the blue points and balls even on that blackened parts.

I put texture detail in low and play without shadows but the same happens.

It seems to happen to other people as well, texture problems , the support people for this game don't seem to be very supportive.

Did you install the patch and the dlc, mcc?

If you did, please do this

http://masseffect.bioware.com/forums/viewtopic.html?topic=643333&forum=127

The first solution deals with missing textures on Therum.

If you have a repair option, clicking on this option in your ME config utility may (or may not) fix this. Deleting the file mentioned in the link will fix it.

As for the support, I agree the EA support is very lacking, but I have seen a Bioware game supported as much as MEP has been. (well, myabe NWN1). Bioware's QA as well as Technical Producers and a few have really been helpfull in fixing problems - together with the community.

The more info on problems the Bioware team on MEPC get, the better they can fix these problems...

Thank you Karsten!

I did install the patch, I'll go to the link.

I have the Repair option and I tried it but didn't fix the problem.

I tried Repair again and this time it did fix it.

I though the lava patches were very small, I am shocked how big they are and that I had manage to avoid several.