It's a big YMMV for all wireless. If someone uses a microwave or has a 2.4Ghz phone, you may get interference that makes you drop packets if you're on wireless G.
As for 802.11b, the technology really changed from when it was first introduced to when G came out. If you get an older wireless b router and adapter, you may not have the same performance you'd get with a newer one.
If you're streaming video, I recommend at least 802.11G and making sure you have a pretty clear path. If you are using streaming codecs, you shouldn't have to worry about packet loss as much because they're made to recover from hiccups in the connection. Streaming video is just made for that kind of thing.
You probably won't be able to max out a G connection unless you're doing heavy non-streaming codecs like DivX. I do recommend upgrading to G from B, if nothing else to get more security support like WPA.