PROM JTAG download cable for Xilinx Spartan II + Webpack

Hi,

    I have a PROM (XC18V02) set up on my Spartan IIE evaluation board. I'm
developing under Xilinx ISE 5. I'm wondering what would be the simplest JTAG
cable I could build (or buy if real cheap) to download my code in the PROM.
Is any JTAG cable supposed to do the job? The fact is I already a very
simple JTAG interface (with a 74HC244 buffer for parallel port)...I tried it
but it didn't work.

Thanks