Hey there guys. I'm thinking about making one of those Lets Play videos, and the game in question is Portal. Can you recommend me some screen capture software? I already have the one that comes with Expression Studio, but would also like to try out something else. One thing to note though, it has to capture the whole screen of 1400*900 at at least 60 frames per second. Any suggestions?

Unless you have some ridiculous rig, it's not going to happen at 60fps. Even with top of the line software you still probably won't achieve anywhere near 60fps at that resolution.
If you can get over that fact, a good software reocrding tool is fraps.

If you have the space you can record a demo of the playthrough (type record demoname in the console) and then convert that to a movie and afterwards add the voiceover.
I say that you need to have space because the way to convert it to a movie is by outputting every frame of the movie as a tga image and the sound as an mp3 which then need to be stiched in another software.
Just google for "source engine record"

Probably Fraps, but it uses up a lot of hard drive space and a lot of RAM. But it's only a Source engine game, so meh.

Xfire is a good free solution, but I've had problems with its codec in video editing software. I don't know whether this is my fault or Xfire's. Fraps is the paid alternative, at $50 AUD. There's a trial if you want to give it a go.
Judging from what I've read, they're both pretty comparable.

Not sure it will fit your needs but . . . CamStudio may be worth checking out . . . =)

Fraps FTW. Anyway, whatever software you use, you should be warned about the fact that it will CERTAINLY give you halved frame rate, lagging gameplay, low fps and more generally speaking very crappy results.
Oh, and DOSBox has an internal feature to record video from games, too, and you should use this instead of a third party software for DOS games.
So said, a advice you to set up a hardware system by using a second PC and the mighty high-definition recorder Hauppauge HD PVR. No lag, no low fps, no crappy results....

Fraps. Record to a different physical harddrive than the one you're playing from. Then use VirtualDub for compression with the newest DivX codec.
You do need to register with fraps, and currently it's about $30.

Okay, people. Thank you for your suggestions. I think I'll just wait a few days or so for Expression Studio 4 to show up on DreamSpark and try that one first, and if it doesn't satisfy me, I'll try the other programs.
I'll be using a second hard disc to store the capturing material. I have an ASUS G71G gaming laptop, so hopefully it will have the power to meet my needs for this project.