Can you describe the computer system a little further (make, model, etc.)? I assume you are talking about a desktop machine, since you mention the sound card and video card. But a P4-1.8GHz cpu in a desktop machine sounds to me like something that would date back about 9 years or so, while Vista was only introduced a little over 4 years ago.
Did you update the machine's original os from XP to Vista? If so, have you seen any performance issues? If not, then I agree with Michael that there is no reason to upgrade, at least until you spend some time trying it with the Perfect Wave. But I would be surprised if an 8 or 9 year old machine with a 1.8GHz cpu could do a good job of handling Vista.
Also, is the 1TB hdd installed as a second hard drive (highly preferable), or is it serving as the main "c" drive, on which Windows and program files are located (which is definitely not preferable, especially in a marginal computer)?
Regards,
-- Al