Have to restart my iMac over and over and over and.... HELP!!!

Question

Since yesterday my iMac C2D crashes continuously (curtain down) and restart is suggested.
I did not change anything nor installed new HW or SW. When trying to use Time Machine for a roll-back, the machine crashes also. I don't know what to do.
Here's a discription of the error report. Hope anybody has s suggestion. I'm lost completely.
Can I re-install Leopard without losing my files?
KR
Rob
Sat Jul 5 23:49:46 2008
panic(cpu 0 caller 0x00321C20): "hfsUNswapBTNode: invalid forward link (0xCEED0018)\n"@/SourceCache/xnu/xnu-1228.5.20/bsd/hfs/hfs_endian.c:254
Backtrace, Format - Frame : Return Address (4 potential args on stack)
0x41667768 : 0x12b0fa (0x4592a4 0x4166779c 0x133243 0x0)
0x416677b8 : 0x321c20 (0x487d90 0xceed0018 0x5a7bba0 0x53b0c0)
0x41667848 : 0x316ca6 (0x41667868 0x6f202e0 0x1 0x203e1e36)
0x41667888 : 0x1fa5ad (0x43483f90 0x6f2a804 0x0 0x0)
0x41667948 : 0x1faee8 (0x0 0x4166796c 0x0 0x0)
0x41667988 : 0x33ef99 (0x5315e08 0x1 0x2 0x48a8dc)
0x41667a18 : 0x32dc04 (0x6f1eb40 0x1 0x1 0x53bc090)
0x41667a98 : 0x1f63a2 (0x41667ac8 0x246 0x41667af8 0x1da567)
0x41667af8 : 0x368cfe (0x6f1eb40 0x33 0x0 0x0)
0x41667f78 : 0x3ddde2 (0x53bc090 0x5b9c860 0x5b9c8a4 0x4303)
0x41667fc8 : 0x19f2c3 (0x57a4160 0x0 0x10 0x57a4160)
No mapping exists for frame pointer
Backtrace terminated-invalid frame pointer 0xb0613348
BSD process name corresponding to current thread: mds
Mac OS version:
9E17
Kernel version:
Darwin Kernel Version 9.4.0: Mon Jun 9 19:30:53 PDT 2008; root:xnu-1228.5.20~1/RELEASE_I386
System model name: iMac5,1 (Mac-F4228EC8)

Answer 1

Have you tried:
1. Booting into safe mode?
2. Repairing the hard drive and permissions:
Repairing the Hard Drive and Permissions
Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Installer menu (Utilities menu for Tiger and Leopard.) After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer. Now restart normally.
If DU reports errors it cannot fix, then you will need Disk Warrior (4.0 for Tiger, and 4.1 for Leopard) and/or TechTool Pro (4.6.1 for Leopard) to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.
The kernel panic log indicates a problem with "mds" which is related to Spotlight. There may be a problem with corrupted indexes or caches. Let us know what happens after you do the disk repair and boot into safe mode.