Hi, I have DL the two iso DVDs of the last Beta version of SUSE 10.3. I have noticed the big difference between both. The SOURCE DVD has 5.2GB and the "normal" has 4.1GB. Why is that and what is the point? And one silly question, do I have to burn the SOURCE DVD on two layer disk? (This really is a dumb question, I should ask if it is better to burn the SOURCE dvd and why?).

The source files are just that, the original source code for the programs available on the first disk. The licenses for most open source software require that the distributor make it available. They aren't necessary for a normal installation (and wouldn't work anyway), they're there for people who want to compile and/or modify the programs themselves instead of using pre-compiled packages.

As for your second question, if the .iso is too big for a normal-sized dvd, you certainly will need to use a dual-layer disk if you want a physical copy. But it's also possible to leave the .iso on the disk as-is and access the files via loopback mounting.