I would urge you to learn Linux in any event. Even if doing so for your own benefit, it can't hurt to diversify your skills.
Learning Linux also means that you're learning Unix -- Linux is a look- work-alike operating system and you would find that you can sit down at a Sun Solaris or H-P UX (and other) Unix systems and be comfortable; the details do vary between Linux and Unix but those are easy enough to become familiar with quickly because the system tools and utilities are virtually identical in the way that they are used. This is not to say that you'll become a Unix expert by learning Linux but rather that you will find a transition from one to the other a fairly easy process; the devil is always in the details but it's easier if you already know how to get where you need to go.
Linux systems are complete. You have everything you need to pretty much do anything you want to -- want to set up a network file system, the software is there; want to set up a DNS server, everything is there; want to set up a LAN, everything is there. You have a Linux system, you have the ability to operate your own IT department in your living room, it's just a matter of scale.
I would recommend that you start with Slackware rather than one of the GUI-based Linux distributions. You learn to administer Slackware, you've learned Linux where, in my opinion, if you learn a GUI-based system you've learned a GUI system, not the same thing. It's just my opinion but I'd rather know what's actually going on than clicking a box and have it hidden from me. Start slow, learn the basics, learn the utilities, learn what they do and how they work together and, well, you'll know things that will always be useful to you.
Get a couple of O'Rielly books (http://oreilly.com/
) on the basics. Take a class. Ask questions at LQ. Take your time.
Mostly, have fun.
Hope this helps some.