not sure about vag tacho.
if its based on the Mk4 platform (98-03 04ish) then you can use the older version or vag com 409.1 which costs around £60 for the software, the down load is free but only allows you access to so much info, but you can get cables off ebay for around £15.
if its newer Mk5 platform based ( i really should learn the model numbers for audi at some point ) then you need to use VCDS which is what vag com became when they switched to CAN software for the newer ECUS. good thing is the softwares free. bad thing the cables have to be ross tech - the company that built Vagcom. as these hold the authorisation software and your looking at around £200 for the cable