"these are some questions that have been running around in my head."
The three major distributions, Mandrake, Red Hat, and SuSE, have options in their installers to preserve user data. These options are unreliable and sometimes sometimes people post complaints on the forum that a distribution destroyed data that should have been saved. Another problem is that the new system may not work immediately and you have to run on a crippled OS for a while.
The way that I handle the problem is I back up everything to CD-RW just before doing the install. Then I install the new system on a fresh partition. I dual boot two Linux versions until the new system is stable and then I copy my data from the old system to the new. If I screw something up I restore it from backup.
Be prepared. Create a LifeBoat CD.