Make sure you are rooted, and that adb recognises the device.
Type the following to download the build.prop file to your harddrive:
adb -d pull /system/build.prop
Open the build.prop file with a text editor and set the following properties as follows:
dalvik.vm.heapsize=32m ro.sf.lcd_density=160 ro.kernel.android.checkjni=0
And add the following line at the end
Save it, and type the following to send the file back to the device.
adb -d remount adb -d push build.prop /system/build.prop adb -d reboot
If you get any error messages after the "adb -d remount" line, then you do not have root...
Edit: fixed missing '=' sign in the 'dalvik.vm.execution-mode=int:fast' line...