If your router supports it, use QoS to throttle the bandwidth on the slingbox traffic. Contact your ISP if you do not know. Most ISPs should help you with this if you use an ISP provided router.
You didn't say, but let's say you have DSL, and he is downloading from you at a rate of 128Kbps (all of your available UPLOAD bandwidth) and you are trying to send out/upload DNS requests (surf the net) or send email (also considered upload), then you will see a major slow down in those areas.
If you have the money and the availability in your area, go with FIOS (Usually at least 15Mpbs UP and DOWN).
Otherwise, go the QoS route and throttle him at 64Kbps or half your upload speed. (google speedtest and take 1/2 your upload speed and apply a qos policy for that amount on your sling traffic). The quality for him will be degraded, but I've watched hours of shows from china at half that rate and considered it tolerable.
Thanks for the reply.
You have given me some info which I can research. Hopefully, I'll be able to better control my bandwidth speeds using your suggestions.
I am on DSL with download speeds averaging 2.3 Mbps and upload at about .4 Mbps. He's using the Slingbox now. I'm getting .29 down and .1 up.
FIOS? If only I could! I live within 60 miles of Silican Valley, Google, and Facebook. 2.3 Mbps second is blazing fast in my community. I see no improvement on the horizon.
Thanks again for the advice.