If linux community was a swimming pool
Debian, Slackware, and Gentoo are the deep end. Suse, Redhat, and Mandrake are the shallow.
Many people prefer the shallows simply because they like the support, and don't have to work to hard at it. Plus they can swim around if they feel like it.
The deep end is were you can dive in if you like it, however sitting on top of the high jumping board can be a bit frightening, plus you can get over your head realy quick. Grabbing on the pool side, gasping for air is never fun, but learning to swim like a seal is.
Goto
www.linuxiso.org and check out the SuSE's live eval disk. It's realy realy cool linux-on-a-cd trial version. Most fun you can have that's under 700 megs. If you like it SuSE has a FTP install option, but unlike most distro's you have to buy it to get the install CD's. Which is worth it IMO if you like SuSE alot.
As far as browsers, here are the main options.
Mozilla -most common, better then the windows version.
Galeon -requires GNOME installed (but not all of it, and you don't have to be running it at the time). Consintrats on being nice to use, and minimises Mozilla's bulk to just a webbrowser
Konquerer -KDE's web browser/file manager. Very slick, not as widely used as mozilla.
Netscape -brought to you by our friends AOL. Mozilla's corporate commercial darkside. Also good, better then IE, but most prefer Mozilla.
Opera -possibly the best browser ever created by man kind. Fast, small, effect, user friendly. The major downside is that unless you pay for it you get a addware version.
Aslo a interesting Distro is "Evil Entity" linux. Not widely used, but it's interesting non-the-less. A desktop multimedia-type distro with a Goth theme. Small stuff, but it looks interesting to me. I am trying to talk my roomate into installing it currently. I was using SLackware, but a power surge took out my harddrive partitions, (freak accident type thing), And I just installed Gentoo (SWEET, but damn long install) this weekend.
For a instant messenger, check out GAIM for all your instant messenger needs. It's supports multiple services. AIM, Yahoo, IRQ, and several others.
Of course you'd want to try out several different styles of DIstro's to find what suits you. But if want something easy and without all the work, go ahead and use Mandrake, SuSE, or Redhat. Nothing inherently wrong with any of them, Redhat is a bit bloated, but their newest revision seems to have fixed that a bit. SuSE is the slickest install I've ever seen (kicks XP's ass), and I never tried Mandrake so I don't know.