A 512MB vidcard will not speed up your system at all. The extra vid memory is nothing more then a sales gimmick. Even Doom3 does not use that many textures. A 128MB card is plenty right now and if you are looking to buy for the long term buy a 256MB card instead. 512MB is a complete waste of money.
As to your origional question There is no special program to find out bottlenecks as they are not the same every time. If you post your current computer and what you want to do with it we can help you upgrade it for your needs.
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Rabyd Rev -- 2 Timothy 2:15
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