If you are only using an old USB 1.1 hub, then I doubt you would get a successful burn even at the lowest speeds (2x?), as the burning software would be continually stopping and starting, and the dvd recorider itself is probably speeding up and slowing down as well.
In general DVD burns are quite fickle, and it is generally recommended that you do not even run other applications at the same time (it is sometimes a good idea to turn off applications that kick-in at schedules times e.g. virus checkers).
A USB2 card is only £15 or less these days. I would add one (useful in any case for ay other applications), and try again. Alternatively, why not fit an internal DVD drive - its easier to do than you might think if you have not done it before.
Also, try other disks as some medias are liked better than others. I have a Lite-on DVD recorder (stand-alone), and it didn't like TDK much, but was fine with Verbatim disks (I would still try the USB first though before changing media, simply to eliminate/conform it as the cause)
