Change the tracks with headset

[leximus2002]

Sorry But You Can NEVER Do That Since Patches Wont Allow The Changes In Way You Use Externet Button i.e Headset, Handsfree etc. An Alternate You May Do Is Purchase Stereo Portable Handsfree HPM-82 - Silicone earbuds offer optimal comfort and sound quality. Use the slim remote control to handle calls, adjust the volume or direct your playlist
Sony Ericsson - Accessories - Overview

you are wrong. when i had my w800 i used a patch to do this. i think it was called: control walkman with headphones.vkp. you could use the button on the headset, which you normally use for answering calls, to skip forward a track in the walkman.
i don`t know if a patch exists for your w700.