Are there any quick rules for playing a Decker in Shadowrun 3.0? I'm looking for like say a long example with notes on a decker running the matrix. As I understand it they work like this.

Decker pulls out his deck and jacks into a jackpoint.
Then he rolls to Logon to LTG.
Rolls Locate Access Node to find their target.
Goes to the target and uses Logon to Host to access. (Begin security tally)
Once inside they can use all host actions. (Each causes a security tally)
Find said paydata and use Download Data action
Graceful Logoff to get out of the system.

Now if they register up a high enough security tally the system reacts. They can fight IC using cyber combat, or whatnot.

There are simplified Quick Decking Rules in Mr. Johnson's Little Black Book (right alongside the Quick Vehicle Combat Rules).

Gnu2, your synopsis looks right but note that security tally starts at the "log on to LTG" stage and carries across to any host on that LTG.
If your looking to play the standard rules rather than the abstracted set that Mystic mentioned, there's a thread from a while ago called the idiots's guide to the matrix (which I failed to find with a quick search, maybe someone else will;)

Is this it?

http://forums.dumpshock.com/index.php?showtopic=90&hl=

Yeah, that's it. Not bad for a target.

It lives! That was a good thread back in the day