That's your problem, you are sharing an (ideally) 11Mb channel for two hops.
Very probably, if you have a good connection, high bitrate, and no interference. It'll still probably glitch occasionally, so it kinda depends on how good you want the result. I'd go wired if you want to do this kind of thing on a regular basis, and not have it fall over when WiFi gets more popular in your neighborhood.
my video/sound is chopy when streaming a 3M bitrate xvid over 802.11b to another pc (with a wifi router in between). if one of the pc's is directly connected to the router the video/sound is fine, im assuming because 802.11b isn't full-duplex. would buying a 802.11G fix that?
Yes. Your problem is the lack of 802.11b speed. If you happen to be getting an 11Mbit/sec connection speed, you'll be lucky if you get about half that in thruput. A highly reflective indoor environment will yield about 3.5Mbit/sec thruput (UDP). You'll be lucky if you can maintain an 11Mbit connection past about 15ft range using typical stock antennas. More than likely, you're access point has slowed down to 5.5Mbits/sec or 2Mbits/sec to try and keep the error rate reasonable. Your thruput will suffer accordingly where you'll get about 30 to 40% of the connection speed in thruput.
Your 3Mbit/sec video rate is presumeably UDP. You can drop packets right and left with UDP and the protocol won't care (or resend). That's the whole idea behind UDP versus TCP which requires ACK's. Full duplex won't make any difference as UDP doesn't need any ACK's coming back from the destination.
If you want reliable 3Mbit/sec thruput, you'll need at least a
9Mbit/sec connection. That's easy with OFDM and 802.11g. It's still half duplex but you will stream much better. At very short range (<
6ft) and a 54Mbit/sec association, you'll get about 25Mbits/sec thruput, which is more than sufficient. For the typical indoor environment, your access point will slow down somewhat. A trick I use is to set the connection speed to some fixed value so that the AP isn't juggling the speeds all the time. I usually use 6Mbits/sec OFDM, but that's a bit slow for your streaming video. Try 9Mbits/sec or perhaps 12Mbit/sec.
Note that you must replace BOTH your 802.11b access point and 802.11b client radio with 802.11g hardware.