This is what the report says:

panic(cpu 0 caller 0x3BB929E0): ext2_dirbad: bad dir (mangled entry)
Backtrace, Format - Frame : Return Address (4 potential args on stack)
0x253cb6f8 : 0x128d08 (0x3cc0a4 0x253cb71c 0x131de5 0x0)
0x253cb738 : 0x3bb929e0 (0x3bbaa72c 0x3bbaa6ac 0x1ec1 0x24)
0x253cb778 : 0x3bb90db5 (0x4ad5a04 0x24 0x3bbaa6ac 0x0)
0x253cb9f8 : 0x3bb92624 (0x4c9f8c4 0x253cbcd0 0x253cbde4 0x253cbf48)
0x253cbaa8 : 0x1e5038 (0x253cbac8 0x253cbf48 0x253cbf48 0x0)
0x253cbaf8 : 0x1ccc89 (0x4c9f8c4 0x253cbcd0 0x253cbde4 0x253cbf48)
0x253cbb68 : 0x1cd4af (0x253cbcb8 0x100 0x253cbcd8 0x0)
0x253cbc18 : 0x1df4c0 (0x253cbcb8 0x43a11f8 0x63 0xd)
0x253cbc68 : 0x1d75ae (0x253cbcb8 0x253cbe2c 0x253cbe6c 0x19a001)
0x253cbe48 : 0x1d7a11 (0x202 0x253cbe6c 0x416f2f4 0x19a001)
0x253cbf58 : 0x37ad83 (0x40b07d0 0x416f2b0 0x416f2f4 0x0)
0x253cbfc8 : 0x19b28e (0x404a9e0 0x0 0x19e0b5 0x3b330d8) No mapping exists for frame pointer
Backtrace terminated-invalid frame pointer 0xbfffcd68
      Kernel loadable modules in backtrace (with dependencies):

Kernel version:
Darwin Kernel Version 8.10.1: Wed May 23 16:33:00 PDT 2007; root:xnu-792.22.5~1/RELEASE_I386

Model: Macmini1,1, BootROM MM11.0055.B08, 2 processors, Intel Core 2 Duo, 2 GHz, 2 GB
Graphics: Intel GMA 950, GMA 950, Built-In, spdisplays_integrated_vram
Memory Module: BANK 0/DIMM0, 1 GB, DDR2 SDRAM, 667 MHz
Memory Module: BANK 1/DIMM1, 1 GB, DDR2 SDRAM, 667 MHz
AirPort: spairport_wireless_card_type_airport_extreme (0x168C, 0x86),
Bluetooth: Version 1.9.0f8, 2 service, 0 devices, 1 incoming serial ports
Network Service: Ethernet (integriert), Ethernet, en0
Serial ATA Device: ST9120822SB, 111.79 GB
Parallel ATA Device: PIONEER DVD-RW  DVR-K06
USB Device: USB Mass Storage Device, Up to 480 Mb/sec, 500 mA
USB Device: Hub, Up to 12 Mb/sec, 500 mA
USB Device: USB Device, Up to 1.5 Mb/sec, 500 mA
USB Device: Apple Pro Keyboard, Mitsumi Electric, Up to 1.5 Mb/sec, 500 mA
USB Device: Bluetooth USB Host Controller, Apple, Inc., Up to 12 Mb/sec, 500 mA
USB Device: IR Receiver, Apple Computer, Inc., Up to 12 Mb/sec, 500 mA

i admit it is a pimped MacMini, but that is not the problem here.

May be it comes from an ext2 fs on the USB-Stick.