I have tried everything I could think of. Also I red most of the relevant topics here. Could someone please tell me how they do it. I have MacBook Pro OS X 10.6 and PC laptop winXP to choose from the computers. I am using Topfield card reader if that matters.
I am pretty much ready to throw this thing out of window.

have you tried it according to the manual?

just copy the files onto the card (which you have to format on the SP first!), paying attention to the sampling frequency of the files (needs to be 44.1 khz WAV or AIFF)... if you have different rates, the SP may pretend not to recognize them.

then insert the card in the machine, turn it on, and it should flash "UAU" (which is SP language meaning 'wow'), then you select a bank, and press the blinking REC button.
(don't do anything/disconnect the power while it's loading after you press rec, or you will fuck your machine up)

hope this helps