With regards to the gym, there are two things I'd focus on:
1.) Stamina and non-impact CV work - this could be building up some serious distances on a cross-trainer, bike and stepping machine, to be included as well as running (preferably outside);
2.) Core stability: building up strength around the torso to make your running become more efficient. These include stuff like the rowing weights, I forget what their name is. Some of these exercises might help, excuse the scary bloke in the animations, I wouldn't want to meet him in a dark alleyway
http://www.beginnertriathlete.com/cm...=486&printer=1
There is also a third: upper body strength, so focussing on toning biceps, triceps etc. Its important to build these up, but not too much (I forget what you need as a long distance runner whether its tonic or twitch fibres, but lifting ridicuously heavy weights counteracts the building of the one you need, think how many sprinters you see with heavy muscles and then look at long distance runners).
Outside of the gym, make sure you're running lots and building the distances up.
Asking at the gym for advice may be a shot in the dark, some trainers are really good, have degrees in sports science and have run marathons before, others are there because they were taken on for summer work and have remained there and don't know much and can't help you with your needs.
You can get a lot of advice off this forum from runners, but to appreciate the runner that you are, you need to go to a running club and get advice from there.