Ok this home made solution isn't going very far.
I have found this for £20 though
http://www.relax-uk.com/product.asp?id=13&sm=14
http://www.bio-medical.com/product_info.cfm?inventory__imodel=6002F
It comes with USB Mini B though, which won't go into a PC and don't think a converter will help.
They say you need this USB Pod for $185
http://www.heartmathstore.com/cgi-bin/category.cgi?item=6002-H&type=store