Mountain Biking - NorCal Converstion Q's: Hybrid -> AllMtn

After searching the forums and elsewhere I couldn't find a solid answer...

The subject: a year 2000 Gary Fisher Wahoo hybrid, stock. Pic here (http://www.flickr.com/photos/atomick/1413361674/). Has both road tires and trail tires.
The rider: Lives in Marin County, birthplace of US mountain biking. Tons of road and commuting experience and plenty of fairly chill trail riding experience. No experience doing super-hilly/rocky fire roads or worse.

The issue: I own a road bike and adore it, but I want to look for an alternative to get away from the traffic-filled roads. I live at the base of Big Rock Ridge, for those NorCalers around...I want to start biking where I've been trailrunning, and even start on some of the basic trails of Mt. Tamalpais itself.

The challenge: Despite seeing a lot of people converting hybrids to road bikes, I want to go the other way...I'd like to outfit this steel-framed, Altus-equipped hybrid for XC and all-mountain style riding (at least by these definitions (http://en.wikipedia.org/wiki/Mountain_bike#Discipline_oriented_designs)).

The question: What pitfalls lie in the way of this plan? Could I put a low-travel suspension fork on the hybrid and just give it a shot - or is that even necessary? If I stick with dry-conditions biking, could I get by with standard stock brakes instead of upgrading to discs? Will I run afoul of inappropriate frame geometry? Is all this so silly that I should sell the stupid hybrid and get an AM/XC bike (loathe to do so, as it makes a great utility bike)?

Thoughts, crew? I'd love to get your thoughts, as I definitely don't trust the local LBS's to do anything but try to sell me a fresh new bike even if I don't need one...

Whew...that's a toughie. I'd prob. keep the dang thing for tame trails b/c you can't get any money out of used bikes these days, and buy a used Trail Bike.

What would be your price range, what are you expecting out of your All Mountain / XC bike?

Do you plan to ride aggressively?
Do you plan to just traverse off road trails?
To you plan to jump very much?
Do yo uplan to do any ledge drops?

Chelboed, all good questions/insights.

- Budget? Great question; if I spend between $300 and $500 in upgrades, I could buy a new Wahoo for that much. I'd like to make the conversion, if sensible, below $300-$400. Otherwise I'd be looking at a new entry-level bike.
- No plans for aggressive riding styles other than trying to make controlled descents down steep stuff, as I plan to mountain bike on trails with peds, horses and FSM (http://www.venganza.org) know what else. Where I live it's nothing but hills so it'd be nice to keep the triple on the hybrid!
- No plans for true off road.
- Absolutely no plans for jumps, drops or stunts.

Buy some nice MTB tires in the neighborhood of 2" or bigger if your frame will clear them and enjoy the trail. I ride an 80's beater Raleigh Pointe on the trails with my daughter on a seat on the back. It's completely rigid an not made for aggressive riding. I think it will last forever for what I'm using it for.

Pete, your familiar with that area. Is there any bicycle friendly singletrack, that his bike could explore in that area?

Of course there is. He's indicated that he's going to be mixing it up with other trails users on different trails though.
Does seem as though his mind is set on that. I like the trails that you rarely see anyone else, myself.

Of course there is. . . . Like this one, eh?

http://www.paradigmhosting.net/images/pct.jpg

That's about 180 miles from the OP's location . . .My bad geography - - forgot it follows the Sierras instead of the Coast Range down there.

I'd love to sneak onto part of it someday.