Let me preface this all with : GNC's name-brand product are overpriced crap. All the other brands that GNC carry are just overpriced. Buy independent!
Glutamine and Creatine are both naturally occuring in the muscle, and in different functions in the muscle. There is no way these two inhibit each other's efficacy (or at least, in no way I've ever heard. If any of you know any evidence of this, that would be quite interesting).
250mg of L-Glutamine isn't ****. You need 5g - 10g of Glutamine in a day. I recommend a tablespoon before or after a workout, and a tablespoon before bed (for muscle repair, which is glutamine's primary function).
Creatine should be taken in equal amounts every day. Really, doesn't matter if you do it before or after a workout (as far as I'm aware) as long as you do it consistently. This increases your baseline creatine levels in the muscle, and therefore gives you more energy for better workouts.
Finally, most "blends" - with the exception of weight gainers, pre-workout energy boosters, and aminos - usually aren't worth the bottles they're crammed in. Buy straight creatine (or better, Kre-Alkalyn) and straight glutamine.
By the way, where did you hear that creatine and glutamine should not be taken together?
Here's a snippet from an article on EAS's site:
Q: If you take creatine and glutamine together, will they compete for absorption?
A: Muscle cells do have what is referred to as a "sodium-potassium pump," a "valve" that allows certain nutrients to both enter and exit. Both creatine and glutamine enter the muscle cell through this pump, however, the actual mineral, sodium has nothing to do with that process. It is incredibly difficult (and by practical means nearly impossible) to overload this pump to the point at which glutamine and creatine would be competing for entry. Neither creatine nor glutamine needs to bind to a sodium molecule for absorption into muscle cells. Creatine binds to a phosphate molecule, which then becomes phosphocreatine. Phosphocreatine is stored in muscle cells to be used as an energy source. Glutamine is a free form, "conditionally essential" amino acid that is prevalent throughout the body. Glutamine is necessary for a variety of functions in the body such as tissue repair and cell volumization. Glutamine does not bind to a sodium molecule for absorption, and is readily utilized throughout the body.