Natasha,
You can buidl PC based oscilloscop, bellow I mention basic components you need. This is the method I have done as a project.
1. Microcontroler (eg:- PIC16f876a of microchip company www.microchip.com)
2. Visual Studio 2005
3. MAX232 level converter IC (price about $1.5 or Rs.150)
4. Serial port cable
5. Step-down transformer (250Vrms - 5Vrms)
If you can find above components I can help you for building the oscilloscope.
send me email or call me on Sunday. sureshd_eng@yahoo.com
+94-776512885
sureshd_eng need to provide a little more information. I know the PIC needs firmware and I know Studio does not had a scope program sample and I hope he has a PIC programmer.
If there a website detailing your scope? I would be interested as well.