Unless you're using a 56k (or lower) connection, then upload and download speeds should be completely independent.
In other words, even if you are downloading at the maximum speed that your connection allows you to, you can still upload at max speed (which, unless you have SDSL, should be lower than the max dld speed).
Consequently, lack of speed can result from
uploaders (=people sending you data) already using most of their upgoing bandwidth to upload to others.
I suggest reading
this. If you still got questions unanswered (which will probably be true), go through the other stickies: there's some valuable info in there...