There's no throttling in the webserver, and there's really no way for a web server to do that, AFAIK. I don't think the POSIX standard for sockets includes that functionality (if I'm wrong, someone will correct me I'm sure).
There's an alternative solution you might consider - $25/month OpenACS hosting offered by one of our community members.
You might also just put your site up on your ADSL line and not worry about it. Frankly unless you get a lot of traffic I doubt anyone would notice. When your folks browse sites out in the world, the vast majority of traffic will be downloaded content. When visitors from the outside world brwose your site, they'll be uploading content from it. The two activities won't really clash in practice.
