Here's a suggestion.
From the sound of it, your data is stored on the same partition as your OS. Save it on to separate partitions, or even separate physical drives, so that if your OS installation goes pear-shaped, you're not worried about losing your data (although I've done numerous repair installations and it's always kept my non-OS data perfectly intact).
edit: damn, I should've read the entire thread before posting... do as Ultra Extreme says.
From the sound of it, your data is stored on the same partition as your OS. Save it on to separate partitions, or even separate physical drives, so that if your OS installation goes pear-shaped, you're not worried about losing your data (although I've done numerous repair installations and it's always kept my non-OS data perfectly intact).
edit: damn, I should've read the entire thread before posting... do as Ultra Extreme says.