You suggest you have broadband connection but then note that the weather can affect speeds. Are you sure it's not a satellite connection? Satellite connection speeds tend to be less than broadband, upload speeds are generally much lower. (BTW some satellite services shape or block p2p file sharing programs.)

Some ISP's tie the upload speed to download speed. ie: the more you use of one, the less you can use of the other. Is this how yours works? Generally most ISP's keep up & down speeds separate.

You suggested a download speed of under 512 .. is that kbps (kilo bits per second) or KB/s (Kilo Bytes per second). ISP's usually quote speeds in kbps whereas LW shows speeds in KB/s. 512 kbps would be just over 60 KB/s.

Are you downloading regular gnutella network files or torrent files?
Downloading torrent files can be greatly affected by upload speeds. Usually the faster you upload, the better your downloads behave.

As a general rule, you can only download as fast as others on the network have bandwidth available. Thus, it's usually best to re-search for the item to attempt to find more hosts for the identical file. And also use the Get More Results tool which helps find more people to download from.