Startup Disk Needs Repair?

I just installed Onyx a short while ago, and the first thing it wanted to do was scan my startup disk. After about 5 minutes of chugging along, it reported that the startup disk needs repair. Then it went on to suggest that I boot from my OSX disc and choose disk utility. There were no other details?

But what will a "repair" do? Am I going to lose data? As a semi-recent switcher, I'm a bit leery of doing this. Repairing Windows in the past always messed up a lot of stuff.

I have a Macbook Pro, 2.16GHz C2D, 3GB RAM, running OS X 10.5.2.

Thanks in advance for your replies.

Z

You won't lose any data. (But you should have a backup, anyways)

"You can also use these even when your computer starts just fine but you want to check the disk for possible file system issues."

The Repair functions of Disk Utility: what's it all about?

Resolve startup issues and perform disk maintenance with Disk Utility and fsck