I just bought an RGV250 shock off of e-bay as I've heard they are a good replacement shock for the GS500.
(also it was 22.80 including postage)

The prelaod is by means of a ring on a threaded section of the shock and a 2nd locking ring.
WHat I want to know is this:
1)  there is a knob in top of the shock that has numbers on it. WHat's this for?
2) the remote resrevoir has a knob on it marked  S<-->F . What's this do?

Soft-Firm? Just my guess.

Those two are the individual adjustments of positive and negative damping. But don't ask me which is which...

Right so I have preload, which is obvious.
Compression Dampening, and rebound dampening.

I guess the S<-->F is slow <--> fast Compression/Dampening.
the other adjuster I guess higher dumber = more dampening?

The shock is from A suzuki RGV250, so I guess it might follow Suzuki standards.
On the GSX-R shock what are the adjustments like?

as per the suzuki shop manual for a 1990 RG-V 250
rebound is on the bottom of the shock
and compression is on the resevoir
there are 4 rebound settings and 20 compression settings
books states to start with rebound in the #2 pos
and the compress in the #9 +/-2

Note:
fully turn the damping force adjuster clockwise to the 0 position then turn out 9 clicks
the STD setting is obtained when the painted mark on knob is aligned with painted mark of the body

what do they do....
1 is soft....
try different setting and see if YOU!!!! notice a difference then set it how you like

Thanks for that
I'll have a go at mounting it this week.