misstery,
How old is your system and what kind of hardware are you running on (processor, memory, video card, etc)? Also, which browser are you using to run the game client in?
Mozilla's Firefox or Google's Chrome browser seem to be the two tht give the best results for the majority of those who have tried them. If you try them out, just make sure you use them exclusively for WGT and don't clutter them with anything else.
Also, make sure to turn all all other non essential programs, and it also might help to launch the game browser directly using this link. Once open, close all other open windows and/or tabs, and run that window all by itself, with the game client loaded directly.
I haven't used Gamebooster for many months, but if it is the same as the old version, you aren't missing anything. Once it runs and clears what it can, that's it. When done gaming, be sure to use the option within Gamebooster to re-enable everything it stopped.