|"Will this be a problem ?"|
The P3-1000 is actually faster than the P4-1400. It should work, but the software may require a CPU with SSE2 support. If the program needs SSE2, you'll need a P4. You'll have to sort that out before buying the product.
"It means Directx 8.1 driver support , not graphics card processing? ? ?"
DirectX is much more than just 3D graphics. Direct3D is only a small part of DirectX. DirectX also includes DirectSound and DirectShow, among many other components.
Most of the time, when a non-3D application requires a specific version of DirectX to be installed, all it needs is the system's sound and video hardware to support the DirectSound and DirectShow components of that particular version of DirectX. The video card's hardware Direct3D functions usually do not matter.
A video/multimedia application calling for DX 8.1 will most likely require a video card that supports the first version of DirectX Video Acceleration (DXVA)--a component of DirectShow. That means a Radeon 7000 or GeForce 2 (or faster). Do you know what video card you have?
From reading the requirements on that page, it looks like they want you to install DX 9.0c no matter what. If Windows doesn't already have it installed, you can download DX9 from Microsoft's website. But as long as your audio/video cards support DX 8.1's DirectSound and DXVA (Radeon 7000, GeForce 2 or better), you should be able to work with standard definition video. Just don't try high definition--you'll need a better CPU and video card for that.
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