I want to try Debian and Slackware. Downloading the first CD ISO of each distro it's possible to startup the system or it's necessary to download all ISOs?

I tried gentoo 2006.1 livecd but it didn't let unfold the menus and I couldn't do nothing.

Is this a question? statement? I am confused.

Not sure what you mean by 'prove' but speaking for Slackware, you could boot the machine using only CD-1. I'm not really sure how much you could actually *do* with only the one CD though. I think most any type of actual installation would require at least the first 2 CD's, unless you managed to do the installation such that everything you chose was on CD-1. Off the top of my head, I'm not able to tell you what's exactly on CD1 and CD2, but in my limited experience, every installation I have done needed 1 and 2. Disk 3 is for multi-language support.

For Debian, I have no clue at all. Never tried it.

Debian netinstall is less than 200 MB download. It will download latest packages as you install.

Kalabanta, It's a question. I feel the ilegibilidad of the text. I have translated by web of spanish to english.

I have been able to startup livecd of gentoo in the computer of the work but it don't convince, visually is similar to Ubuntu but with less services of administration initially. Perhaps at another moment I'll test Slack or Debian. I wanted to study other alternatives.

I don't use Gentoo, but I know for a fact it is more customizable, stable, and powerful than Ubuntu will ever be. The reason they look similar is because of the GUIs, but whats running in the background is what really counts.

Kalabanta is absolutely right.
Gentoo is also most breakable, unstable and frustrating distro. It all depends on user. In Gentoo you are the installer (forget the LiveCD, it's not for newbies), you are the maintainer, there is a plethora of things you as user have to customize.

I think the OP is after live CD versions of Debian and Slackware to try them out. Slackware doesn't have it's own live CD as such, the disks are just for installing. Try the Slax Project - it's a very popular and powerful live CD. For Debian, I'd suggest getting Ubuntu or Kubuntu or Xubuntu (they are all the same but with different desktops) - they aren't strictly Debian but have that as their base and look and work in a similar way to the latest versions of Debian.

If you want to try Gentoo, get Sabayon Linux - it is a beautiful looking system and runs from the CD.

Funny.

@ GrapefruiTgirl:

Hm.. what about Slackware 10.2? IIRC The 2nd cd was needed for the initial 2.6.x kernel (as it contained modules, alsa-headers, and some other stuff). I have not tried Slackware 11 but I don't think "at least 2 cds" are required by anyone who wants to do anything with Slack.

@ kalabanta:

If you don't use it how do you "know for a fact"?

Mhh.. Another "fact" which comes from your ability to tell the future?

I'm not trying to be rude but newbies are very impressionable.

It's a known fact that 99% of the times when someone starts a phrase with "it's a known fact" they're actually expressing an opinion and hope it sticks. [not original, stole it from someone here on LQ, can't remember who]

I don't understand anything but the conversation seems very animated! Damn it's my ignorance of the language!

Then as comparative Gentoo is better than Ubuntu? and Slack?, Debian?

My idea was to try other distributions without crush Ubuntu again. For that reason the livecd. I understand that my idea is difficult if I don't install the system really don't take advantage of it completely. To spoil self!

@ reverse : What point exactly are you attempting to make to me? What ABOUT Slack 10.2?? Regardless what you 'think' or I 'think', if a 'newbie' were to want to try Slackware, for example, why would you (or anyone) imply that they should install an older-than-newer version, AND to try it with less than the entire disc-set?? You apparently have some knowledge I don't have, so since I too am a 'newbie' to linux going on 4 months now, please enlighten me.
As for LiveCD's, Slax is btw an excellent place to try a Slackware-BASED distro, but when I made my offer of assistance, I was under the impression that the OP wanted to try Slackware, NOT a Slack-BASED live CD.

Dissident, you will invariably get a different opinion from every user here on what's "the best". It depends what you want to do with it, and how much you are willing to devote time to learn the distro you choose.
I prefer Slackware, for many reasons. If you are looking to see the ins and outs of each one, check out www.distrowatch.com and/or the Home-Page of the distros you are considering. Using Google, you can quickly locate the homepages of most any Linux version there is out there.
Best of success to you

If they all were the same there would be no need for multiple distros.

Ubuntu - relatively bleeding edge, thus not the stablest. Easy, newbie-friendly, all system-level customization is done by developers, user has no choices here.

Debian (stable) - packages are not the newest, rock stable.

Gentoo - everything is customizable, starting with compilation options. To enjoy Gentoo above average Linux knowledge is required.

GrapfruiTgirl, I consider that is not exist distro better. The mark the necessity of the user. But like we have entered the dynamics of which gentoo is more powerful… 'Gentoo is also most breakable, unstable and frustrating distro.'

It's a subject very beaten but always he's interesting to discuss on the distros.

Exactly, Dissident_0 A person must start with something they are comfortable with, and as they gain experience, or have more demands, they can upgrade easily to something more powerful. I 'tried' Gentoo at the very start when I started using Linux a few months ago, and I was discouraged. It may well be a powerful, capable distro, but it IS complex.
Slackware also is powerful, stable, and very capable, but it does require a fair bit of tuning to get it exactly how you want it to work. It is an excellent choice for someone wanting to take the time needed to learn more about Linux in general, rather than learning more about only ONE distro platform.
The Live CD's of ANY distro are a great way to test-drive a different type of Linux without crushing your existing Ubuntu installation.