Sir Sandslot,
Your ISP advertises speeds in kiloBITS per second. Limewire displays speeds as kiloBYTES per second. There are 8 kiloBITS per kiloBYTE.
Sooo...
768/8 = 96 kiloBYTES per second as your maximum download rate.
But...
Your download speed depends on how fast others upload to you. This includes their speed and how much bandwidth they are dedicating to uploads. It also depends on how many hosts you are downloading from.
Have you tried running a speed test to see if you can actually achieve 768 kiloBITS per second?
Speedtest.net - The Global Broadband Speed Test
If you want any more help, please click on the link in 6pac's post and give us the details of your setup.
Good Luck
Dan