If you have an older system that can run real-mode DOS (Win9x or earlier), and you have an ISA-bus Sound Blaster or ESS card, you might want to have a look at my Daqarta package. You can even build your own "card" from a handful of resistors hung on the printer port, if you don't have one of the above cards. It will be only 8 bits, same as many digitial scopes, but unlike the sound cards will go down to DC. See the LPTX driver info on the site.
The Windows version of Daqarta is in the works.
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis Shareware from Interstellar Research