It's pretty much the same for 10.5.x
"Try Disk Utility
1. Insert the Mac OS X 10.5 Install disc, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at the top of the screen. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3. Click the First Aid tab.
4. Select your Mac OS X volume.
5. Click Repair. Disk Utility checks and repairs the disk."
http://docs.info.apple.com/article.html?artnum=106214
Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.
(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)
Tough without the Install disc, but some things to try...
Does it boot to Single User Mode, CMD+s keys at bootup, if so try...
/sbin/fsck -fy
Repeat until it shows no errors fixed.
(Space between fsck AND -fy important).
Resolve startup issues and perform disk maintenance with Disk Utility and fsck...
http://docs.info.apple.com/article.html?artnum=106214
Does holding the Option or alt key bring up the Startup Manager?