1) To update the pre-installed Swype to Swype beta you have to have root access or else this isn't going to work
2) Download "Root App Remover" and "Root Explorer" from the android market
3) Run Root App Remover (it will take a minute for it to initially scan the phone for system and user apps)
4) Using Root App Remover go to system apps scroll down to Swype tap it and press recycle, to completely uninstall it (which you have to do) press menu then "SystemApp Recycler" and uninstall it.
5) Run Root Explorer and press the "Mount R/W" button at the top if it isn't already selected, after that to go "system" folder then the "lib" folder and delete the file "libswypecore.so" (if it isn't there then go back into system and then back again)
6) After that go into the "data" folder then the "data" folder and delete "com.android.android.inputmethod" file (if its not there then quit root explorer)
7) After that go to the Swype Beta Website and register, go through all the various steps untill you've finished downloading and installing the Swype Installer.
8) Run Swype Installer and go through all the steps, then download and install the Swype Beta, generate the license using the installer and your done the newest Swype beta is now installed one you Samsung Galaxy S
Sorry if this guide is too long i just tried to explain it in detail. I Hope this guide helped you install the newest Swype beta, if you have any questions feel free to ask i'll get back to you as soon as possible.