Here is the how-to guide for multitouch (dualtoch) on SonyEricsson Xperia X10:
Download latest flashtool here:
Download the FTF-File for Flashtool Version 0.2.4 or higher:
Copy this File into the firmwares folder directly, and copy the “Dualtouch” Folder inside the Firmwares Folder of Flashtool. After that just flash your device and reboot, if the ROM is capable of Dual-/Multitouch you will have it now.