Using a PC to capture, manipulate and display a signal sounds very attractive. There have been several cheapo ideas using the sound card of a PC, but the resolution is only down to KHz, and the more professional digital oscilloscopes use the USB port and have a resolution into the MHz, but these cost from £200, and typically over £1000! It may be better to use a PIC for this, in which case this project becomes a PIC µController project, but the resolution would only just get into the ms/s. As an initial outing a sound card scope may be a sensible introduction.
Another approach might be to hook an analoge-to-digital converter to the PC parallel port.