you ALWAYS run a risk of loosing data when you partition your drives, though most of the time it is small, it can happen. think of partitioning your drive like getting surgery, when you get surgery, there is alway a risk of complications, and in extreme cases death, well this is like surgery for you HDD. you are opening it up and changing around the partition table, so there is a risk of data loss, but as long as you are careful, that risk is very very small. if you do not know much about partitioning, i recomend you do some research on the subject, and not try partitioning your drive. i think the best thing for you to do is install another HDD, and use THAT one for linux, then you just have to select it as the target drive for linux to install to, and the installer will do the rest. i hope this helps out some, and doesn't deture you from Mint, or any other Linux distro, it really is great.
good luck and if you have any other questions, just post up and someone will do their best to answer them.