going to do my first product shoot

[AF44]

ok so through a friend of a friend i got hooked up with a new skate company who wants me to do some product and skate shots. they want to take the product shots at night, and my film camera doesnt cooperate well with an external flash... im borrowing a canon 420ex speedlight to go with my canon elan 7E, and when i attach the speedlight, the exposure numbers stay the same, just as if the flash wasnt even there... im guessing i would have to adjust the settings manually to get the shots that i want, but i think that if i try to eyeball the settings that the shots could come out bad, and there goes my photography job... im looking into borrowing my friends DSLR and flash, which would work ok short term but i cant always be borrowing his stuff... im more interested in getting my speedlight and elan 7E to work together in cooperation. so is there any settings i need to change on the cam/flash so that the exposure will change accordingly when i attach the flash?

also, any helpful tips on shooting model shots outdoors in the dark would be great. thanks :]