Hi, I need help buying a new bike.

I haven't been mountain biking in some time now, probably about a year now. Partly due to the fact that my bike is an old ( about 1998 ) Kona Firemountain. I think its time I bought a new bike.

I have heard about something called "auto-lockout", wherethe shock tells the difference between rider input and track input and locks the shock out accordingly. This sounds good because ( from what I hear ) it combines the effeciency of a hardtail ( which I like ) with the travel of a full suspension bike ( which I also like ). Can someone tell me about this "auto-lockout". Is it fairly common/expensive? And can I buy a ( cheap ) frame and put auto-lockout shocks on it?

Anyway, I don't want to spend to much money and I don't mind a secondhand bike thats a couple years old. But I would like a bike with a full suspension and disk brakes and a fair bit of travel but not a downhill bike.

Any input is welcome, thanks.