why repartitioning a disk involves so many risks?
The risk is usually due to the person partitioning not being familiar with the process. It isn't any more risky than a lot of other things we do with computers. I'd suggest a little reading on partitioning.
One problem many windows users have is understanding the difference between drive and partition since windows seems to use these terms interchangeable, hence adding to the confusion.
I'm not really sure what your question is, a good choice for a newbie for what? The number of partitions? size of partitions? formatting and creating filesystems?
Puppy is pretty easy to install if you have some knowledge of Linux and in addition it is very small, doesn't take up a lot of space. It would probably be a good idea, particularly if you are not familiar with creating partitions, to load Puppy as a Live CD, open a terminal and run the command fdisk -l (lower case Letter L) in a terminal to get your partition information and post it here so you can get specific advice.
If you have windows installed, especially if it is an OEM, you probably have one large partition, maybe two if you have a Recovery partition so the fdisk info would be helpful.