The speed of a DSL link is measure in multiples of bits per second, while your file download speeds are measure in multiples of bytes per second. 1 Byte is 8 bits, so if you are getting 1Mbps (bits per second) then that is equivalent to 1,000,000 bits / 8 bits (or one byte) = 125,000 bits per second or 125 Kilobytes. So your 100KBps is not that far off the mark.
If you want to have faster downloads then you would need to upgrade your ADSL. If you wanted 1 Megabyte per second download then you would need a broadband ADSL link of around 8Mbps or greater.