Bike advice please

Teach
Teach Posts: 386
edited November 2010 in MTB beginners
Some of you may have seen me on the road bike section, but I am new to MTB.
I have a 5 year old specialsed hardrock sport. I bought it to go on canal paths etc with my children. Last night I was invited out through a friend of a friend to go on some forest trails, bridleways fields etc What a buzz.
My question is what do I need to do this sort of riding on a regular basis.
They were all riding £2000+ bikes. Didn't get chance to ask any questions yesterday but today the questions start!
Is my bike good enough? Do I really need full suspension (I didn't find the ride uncomfortable.)
Is it worth upgrading this bike eg new forks and change of brakes? I'm fairly competent, having just buit my road bike from scratch.
Do I start again?
With my road bike I knew what I wanted, type of frame, then manufacture, brand of gears then spec it was relatively easy. However MTB there seem to be so many variables. I really don't know where to start. I'm not looking at spending thousands . Ideally less than £500, but I also know what I'm like and if spending up to £1000 does buy a significantly better bike then it would be worth doing because I will aways wish I'd spent just a bit more.

Current bike spec fork RST GIla 100m travel
Tektro linear pull brakes.
I'm not looking at racing just getting out with some friends and having a good time.
Than you for taking time to read this and any comments would be appreciated.