Are you sure there were no plugins missing on the new setup? If not, you should look into using some plugins anyway,
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Also check to make sure your Windows XP service packs and updates are the same. I think you can see the hotfixes in Add / Remove Programs. Are you using the ASIO drivers for your sound card? Are those drivers the same version? It's not going to be a hardware thing, it is going to be a software thing. The only possible hardware thing would be access to more resources, and how your software utilizes it. If you are using EQ plugins, maybe this is the case, but I don't know many companies doing resource saving without you explicitly checking a check box or selecting a light version of a plug.
If it helps your sanity, here's a brief review of the fundamental architecture of every modern computer. The five classic components of a computer are the processor, memory, input, output, and datapath. The processor gets intructions and data from memory; input writes data to memory and output reads data from memory. The sixth element is control (software, OS, drivers, audio apps, plugins, etc.). Control sends the signals that determine the operations of datapath, memory, input, and output.
Hardware is an underlying substrate to push digital signals through on. The basic components don't manipulate the data without the software (control) to tell it how to manipulate it.
Best of luck.