In LW's Library, you can delete incomplete files. See if the torrents are there first.

Also, if LW has been running for a while, Virtual Memory can grow over 1.5 GB. A restart of the machine usually starts fresh, and recovers about 1 or mor GB of free space. If you don't want to restart, just Quit LW, and run another java application, like Apple's Java Web Start.app (it's in the Applications/Utilities/Java folder)