Having said that…
The first time I played GTA IV online, there was only one other person there. This, I suspect, was the problem; they were solely concerned with killing me.
I played a few games yesterday afternoon, and actually managed to win two and hold my own on another. I believe this was related to the fact that there were around 4 people this time, so they were distracted with killing the others and I was able to prepare myself and get a few good shots in.
This does, unfortunately, mean that the expiration of my 1 month Gold trial is now a problem again. Damn you Microsoft, and your evil money-grabbing ways!