BitTorrent downloads shouldn't really affect your KDE session at all. What client are you using? If you use btdownloadcurses, it'll take 1 to 2% of your CPU. However, something like Azureus is much more resource-hungry. Also, although you might now be downloading, you might be uploading. If you don't put a max upload speed, you could find that your entire bandwidth is being used to upload. You should probably set your max upload speed to 30-50% of your bandwidth. So if your bandwidth is 30 k, you'd do something like:
Code:
btdownloadcurses --max_upload_rate 10 your_torrent_file_here