To increase the number of simultaneous uploads possible, go to TOOLS > OPTIONS > UPLOADS > SLOTS and increase the 'Start Upload Slots' and 'Max Upload Slots' to about 5. Of course, if you are using something faster than 56k dialup, make the numbers larger - M U C H larger.
:-)
If your downloads are failing even if you don't have a firewall or anti-freeloading features turned enabled, then I cannot help you any further. Sorry.