PC Based Scopes

A nice project is to venture and build a pc scope. And could be useful and a good money saver for a beginer to obtain a scope and to conduct a few basic experiments? Has anyone ever conducted experiments or tried some of the scopes present ond the net like xoscope on linux. I would appreciate your help guys i also fond this link below intresting but i bet it needs some additions and explenation for it to at least capture 25v preferably +/- what do oyu think?

http://home.planet.nl/~m.f.hajer/scope2k4.html