Start the client with the option "-bind=127.0.0.1". You can connect to another people for download but another people cannot connect and download from you.
FaSan
I'd really rather use NetBalancer to rate limit bitcoin-qt if I were going to do that than kill connections altogether. Which, imho, really ought to be built into the bitcoin-qt client, but that's another matter entirely. I'll do that if it becomes necessary, but so far, most of the problem - I think the hard drive upgrade / replacement mostly fixed the problem.