Will adding extra RAM in my computer speed it up?

It depends on how you're using it, and where the bottlenecks are - I have an identical model, sans the stock video card, and with a new hard drive and it works fine. My installs of windows XP and 7 are from scratch, however and don't have any crapware on them. One very simple check to see if your issues are due to ram is to look at process manager and see if your memory usage is above average.If the system is not ram bound, then adding more ram wouldn't help much.

You may also want to run a hard drive benchmark to check the hard drive. You can also check the hard drive with hdtune.

I might also suggest running xperf, which should give you an idea of what exactly is the bottleneck.If you're on xp, you will have to run xperf on the system, then move it over to a 7 or 2008 system to view the graphs

In short? Adding ram MAY be a good thing, but it wouldn't double the speed, and it may not be the ram. Without a little poking about its hard to know for certain what exactly is the bottleneck.