Some questions before I install FreeBSD

1. Can I dual boot FreeBSD with linux distros?
2. What is this ports thing? Is it like Gentoo's Portage or apt-get? If so, can I just do ports-update and ports-install xxx ?
3. Does it have good support for linux programs? Is tar.gz installable?
4. Is the kernel compilable? If so, is it similar to the linux kernel?
5. How does sound work? Through alsa?

Thanks

1 - Yes
2 - I believe it's closest to portage - you get a directory structure with a directory for each port (under a more organised hierarchy, not just a flat list). You change to the directory of the app you want and type make install and the source code is downloaded and built (along with any missing dependencies).
3 - There is a good linux emulation system, but I don't know if *everything* works. Tar.gz is generally source code for Unix as opposed to just Linux, and will usually compile.
4 - The whole system is compilable, but I haven't had much experience compiling just the kernel.
5 - Have to leave this one for someone else, sorry... I never got around to setting up sound before my hard drive died (I was only testing BSD, never got to use it too seriously).

2.http://www.freebsd.org/doc/en_US.ISO...rts-using.html

This system works great.

3. http://www.freebsd.org/doc/en_US.ISO.../linuxemu.html

4. http://www.freebsd.org/doc/en_US.ISO...nelconfig.html

5. http://www.freebsd.org/doc/en_US.ISO...und-setup.html

Freebsd is very well documented, I can't speak on the other bsd's, as I've not used or installed any of them yet. The freebsd handbook is about the best guide I've seen for an os. I hope these answers are not misinterpreted as short, but, a quick link to an answer seems so much quicker than typing in info that's already available. Hope it works out for you.
good luck.

Yes, as Peacedog has pointed out FreeBSD is extremely documented. Consult the handbook, manpages, mailing lists, etc. Probably 90% of your questions are answered some where deep in these mediums.