Welcome to CD Freaks!
It doesn't hurt to just put the drive where the old one was.
But if you have problems initially I would recommend putting the 812S on the secondary master IDE channel (IDE channel #2 as "Master"). If you don't know already there are jumpers on the back that set whether or not the drive is Master or Slave.
Sometimes you may have problems if you are not using an newer 80 wire IDE cable, so if you have problems to start with, try replacing the old IDE cable. If everything works fine though, don't worry about it.
I would use (actually do use) the bundled RecordNow software to burn DVD's as it seems to have allot less issues then Nero with the 8xx series of LiteOn drives.
It will be on the Sonic CD that comes with the drive. For some reason sometimes it is "hidden" on the CD. Check here for how to find it if you have problems.
If you have any further questions please drop by the LiteOn forums for more information/questions on your drive. The LiteOn 812S is a very new model and I look forward to hearing more insight on it.
There is a LiteOn tools guide in my signature that you may want to look at. Some of the tools should work with your 812S
There are many informative "stickys" all around these forums. Take some time and read around an I'm sure you will learn allot