I'm not a tech savvy guy too but I would like to share my humble experience with you.
I'm not sure if you are using both of your PCs under the same home network? (Meaning both PC are connected to your home wifi and your router is attached with your WD My Book Live)
Assuming that it's, you should be able to view your My Book Live as a "Drive" on your two PCs (Without the need of WD2GO). With this being the case, you should be able to play your video files just fine on both of your PCs without too much speed issue. It's just like attaching a portable hard disk drive to your PC.
If your two PCs are in two different locations, then that means that you are accessing your My Book Live from an external network to your home network. With this being the case, you will need a decent upload speed from your home and good download speed from the location of your second PC for WD2GO to work properly. I can't tell you how much is decent upload speed but I once tried viewing my video using iPhone on 3G (About 3mbps download speed) for a 700mb file and it's choppy and can't stream very well. My home upload speed was about 0.5 mbps.
I hope this experience of mine is of use to you