Heh, I do support PCs for a living, so I don't think I'd be surprised about the number of processes running in the background. Unfortunately your screenshot is completely illegible (and that doesn't look like the task manager, what is that?), but it looks like you only have ~22 processes running there. That's not unusual in the least, but besides, it's not the number of processes but what kind they are and what they're doing. The reason I said that I couldn't think of any other troublemakers is because after AVG and Windows Updates, I couldn't think of any automatic processes that came from things you didn't know about. So, I was saying that you should simply take care of the problem tasks, rather than try to somehow kill multitasking.

Besides, there's a number of ways to suss out undesired processes, if you're really worried about it. The best tool I know of for this is Process Explorer. It's a Microsoft tool, but they didn't develop it. Task Manager is light on the details for running processes, but this should give you more, or at least it's easy to Google a process from within the software. After that, if you identify any troublesome software, you can go about uninstalling, changing settings, or forcing those processes not to launch through something like msconfig.

*edit*
And of course, the best solution to all of this is to get a new PC that will handle this stuff better. There's a Core i5 system (with 3GB of DDR3 RAM) from Dell for $650 at the moment. Pretty good.