Possibly the most `dangerous' question to ask about Linux.
Lilo is pretty good at finding boot sectors on other partitions, and the only OS it *probably* won't find in my experience is FreeBSD. But taht is Ok because FreeBSD has it's own boot manager that is pretty spiffy.
Linux Distro's is another question. Just keep in mind that if you use Red Hat, Suse, or Mandrake; you will be learning Red Hat, Suse or Mandrake. Linux is really *just* the kernel and nothing elese. All of the rest of that stuff (directory structures, package managers, init scripts, and such) can be pretty disparate from one distrro to the next, although they are all similar enough that once experienced at the command line, will be a pro on most Distro's.
To Linux newbies I always say 'Dive in Deep' and try 'em all. This is for two reasons. One - you will most likely decide on your favorite based on *your* experiences not somebody eleses. Two - there is so much to learn. I frequently get new users in my Linux User Group that have used Red Hat for 1+ year and don't know how to untar and compile software by hand ( a pretty basic *nix skill) because they have alway used RPM's.
Here is a great place to download/burn iso's of some of the more popular distro's. http://www.linuxiso.org
<opinion>
But since you asked.... I like Slackware the best. It is fine for newbies. Sure the learning curve s pretty steep compared to other Disto's, but that just shortens your time to becoming experienced.
</opinion>
