I have finished the framing and I need to run some lines from the trunk lines into the newly added rooms in my basement. I built soffits around the main/trunk lines and I'm wondering if I should have done the HVAC ducts first. I thought I'd run a rectangular duct through the soffit and just put the vent cover right there on the side of the soffit. Does this sound do-able and what kind of hardware do I need to cut into the trunk line and add the new ducting?
Help!

Does this sound do-able and what kind of hardware do I need to cut into the trunk line and add the new ducting?
Yes it should work.

You will need sheetmetal for the duct and snips, drill,screws,grills,s hooks and drives if rectangular duct, ruler or tape measure,hammer ETC

Metal duct is great ! But flex duct is cheaper and easier to install . You will need 1-start collar, box of flex duct 6" or 8" panduit straps,mastic,tape panduit tension tool, for flex duct. And just as hvac1000 said for metal duct. You can get all this at Home Depot

Thanks guys for the help. I'm definitely a novice here. What is a "start collar" and how does it go in, and "Panduit straps" and "Panduit Tension tool" and "mastic"? I know what the flex duct is.
Can someone tell me how to post pictures on here with my posts to show people better what I'm talking about? I'm not sure how to describe my situation in detail, and I think pistures would make it a lot easier to explain.

Your best bet is to get a book or books from the library to help you cover all the aspects of duct work. It would be impossible to lay out your whole system here. You just need basic info and books can do that.

HVAC1000 is right it would take way too much time to explain all you need to know about laying out your duct system here. Im sure all want to help anyway we can but sometimes things are just to detailed to put in e-mail form. Here are some sugested book sites you may find helpful. 1. BOOKS4HVAC.COM 2. RHVACTOOLS.COM 3.The ESCO Institute
A start collar is just what it implies its asheetmetal collar which goes into your supply trunk to start the flex duct run. Panduit straps are the long nylon straps used to fasten the flex to the collar, Panduit gun is used to tighten the panduit straps onto the collar. Mastic is the paste like substance used to seal up the duct where you cut in the new ducts and other places that need to be sealed. But just as HVAC1000 said your best bet is to get the books if you want to purchase them you can go to the sugested sites or just visit your local library.

Wanting to do all this on your own is great,, but,is the furnace going to be big enough to take care of the extra square footage? If not you may be getting ready to hurt yourself,if not done right,ypu can very easly take away the heat from other parts of the house.

Yeah, I thought I'd keep most of the vents down there closed unless it gets too warm or too cool. Right now, there are 2 vents down there that stay closed all the time and it stays comfortable to me. My wife will probably like it warmer but it's kind of like my Man-cave and I don't think she'll be down there much really.