I found an old galvanized steel tub that i want to plant some veggies in. It is quite rusted on the bottom. Will the rust hurt the plants or effect the safety or taste of the veggies?
I don't think you need to worry. Rust is iron oxide, which will add a small amount of iron to your potting mix, which is not a problem. Galvanized steel is coated with zinc to prevent rusting, so if that is what your planter is made of, it must be very old or battered. I was curious about your question since I've considered growing in galvanized trash cans. I found the site below, which reassured me.
Here is a link that might be useful: Is galvanized steel harmful to the soil?
Just to ad, you need to be aware of the heating effect of metal containers - they can cook the roots of your plants, especially in full sun.
I was gifted a couple of large pepper plants (at least 4 or 5 years old) in an old dryer drums. Yes, really. Fortunately the grey enamel and the punched holes all along the sides prevent heat build up... and the peppers are thriving.