Most of Vox Studio's algorithms are tuned for accuracy and speed. Vox Studio does a huge number of calculations (tens of millions) for every conversion or filter operation. This is done using the PC's CPU. No additional hardware is required. Vox Studio really shines by the quality of its conversions and by the amazing speed at which they are performed.
A 100MHz Pentium is probably the lowest acceptable platform for Vox Studio off-line conversions, but it is the bare minimum and may be too slow for real time operations on file types that require complex algorithms. Of course, the faster your PC, the better. A 400 MHz Pentium or better is the ideal platform for Vox Studio to really fly. Vox Studio is so optimized that most filtering operations are performed faster than real-time.
If your PC is very slow, you will still be perfectly able to perform any conversion you want. You may, however, hear pauses (jerky interruptions) when playing back some telephony format files on that PC's sound card. This is simply because Vox Studio decompresses the encoded files on the fly and these decompression computations will take more time on that PC. The machine needs to stop playing sound to allow your CPU to catch up with its number-crunching. The more complex the compression algorithm, the more likely this is to happen. In summary, speed is critical only if you want real-time playback of compressed files or complicated recording operations, not for conversion. As the computational speed of PC increases with each PC generation, this becomes less and less of an issue.