There are lots of people who got size mismatch error while installing Winterboard, etc through Cydia. Why size mismatch occurs in Cydia? Well the answer is, its due to source link error. In cydia you can fix size mismatch error by following steps below:
Step 1: Open Cydia and Go to Manage Button.
Step 2: Select Sources and Tap edit button.
Step 3: Click on Add button and In url section enter http://cydia.hackulo.us and click on Add source button.
After adding the above source, the size mismatch error will be gone. You can try installing Winterboard in your iPhone.
Till then Happy JailBreaking!!