I would imagine that a simple microcontroller + simple analog circuit could be fashioned to make any necessary conversions (even frequency measurements), then ship it out as serial data. I did a project for my college physics class that did something similar. I used a Motorola 9S12DP256 (68HC12 family) <-> Macintosh LC III modem port. I used RealBasic, which was very inefficient, but it was so easy it was like writing a HyperCard stack. All serial communications are already taken care of on both sides, I just called send and receive functions! Communications were able to go in both directions and it even used XON/XOFF handshaking. The LC III had a VRAM upgrade to take it to Thousands of colors at 640x480 for the presentation. This "machine" was interactive with the projector and the actual physical parts! Here's a page about it:

http://www.d.umn.edu/~bold0070/spymac_mirror/projects/goldberg/