Theoretically 1mbps of transfer would equal about 320 gigs.
BUT, if you have a line capped at 1mbps and use all of it all month your site will be unreachable. (If you're going to cap your line you need to cap it about 40-50% higher than what you actually plan on using in order to handle traffic spikes. That's why capped bandwidth is cheaper than non-capped)
I had a box at datahosters for a short while. While they were very helpful their network problems, or problems with verio forced them to cap my line at 10mbps.
I was running paid listings on the Hun and the page was virtually unreachable. (I have a page today doing 44mbps)
They apologized and offered to move me to another provider that would match their prices at no charge, but I just went ahead and moved all of my stuff to
Techie Media
You should also know that their dedicated plans are "unmanaged" services. They give you a server with software installed and an uplink, but you have to set up your sites, email, log rotation etc. yourself. So you better know all of the relevant unix commands.
If you know how to manage a server and they have their network issues ironed out they're not a bad choice.
Even though I was very unhappy about their network issues (read: capping my line) they handled it right from a customer service point of view by offering to move me and saying they were going to issue refunds for the problems caused by it.