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Having not found anything on it in their support forums (the search function there is awful, by the way), I suggest both posting in their Technical Issues forum at www.pokemontcg.com/forums as well as submitting a support ticket with them at support.pokemon.com .
I'd appreciate it if you got back to us with any answers for solutions they give you, so I can have a better idea of what to suggest to others in the future, because quite honestly I'm not having these issues with my client on my PC with the following specs:
AMD Phenom II X3 720 (triple core 2.8 GHz processor)
8 GB DDR 2 RAM
ATI Radeon HD 4300 with 512 MB video ram
The client is still fairly clunky and slow, however, and I think a lot of that has to do with how much client-server communication is going on behind the scenes with the game. Far faster now than it ever was last year, though.