Probably a bit late but.. 8260 JTAG and BDM functions are muxed I think. You need to take special care over the PORESET line which is connected to the JTAGTRST line internally.
TRST must be high throughout JTAG/boundary-scan testing.
Free JTAG software ? Try teh Buzz module from www.jtaglive.com works with Xilinx cables too provided you have the latest version of their iMPACT software installed (ask me how I know ). Buzz is great for continuity testing and has a neat watch feature to sample
a pins activity.
Cheers
Des