Sure, anything that will hold water, although I think those rot out after a while if I'm not mistaken.

i dont think it should rot...its aluminum not iron. or well i guess i have found really really old soda cans in the ground that seem rotted. but its not going to be for like years so it shouldnt have that much time. i was just worried about it possibly adding minerals. but probably no more than plastic adds petroleum?

I think you could go with your pie tin without any problems. I have no problem with plastic though -- plastic is stable so won't add any measurable petroleum contamination... it's precisely this property that makes plastic so persistent in the environment. So, your choice, both are fine.
-Don

thanks don, and tommy, the only problem I have with plastic is finding something that fits in the space i needed without being too small. I looked for glass but found nothing. also i sculpted an aliens theme on the pie tin so it looks pretty sweet. and I'm using nontoxic waterproof sealer on it and another pie plate between them to keep it from touching and make it more sturdy.

So long as nothing with copper, magnesium, calcium, or fertilizer products, like potassium or nitrogen, come into contact with the plant's soil or water, your fine. The fertilizers rot the roots, the mineral salts change the soil ph and kill the plants, the copper is an allergen to most carnivorous plants. I have heard of no adverse reactions from aluminium, so have at it.