Simple Solution
Just came across this question, and although the original individual who posted it probably figured it out by now, I just experienced this problem myself and found an easy-to-use solution that isn't mentioned on here.
The file that appeared in my trash and that would not delete turned out to be caused (at least in my case) by some sort of problem with the .Trashes folder on the bootcamp partition (that I use to occasionally boot the computer in Windows XP Professional. If you boot your computer into XP, click on the C drive (which should be titled "Boot Camp"), go to tools, folder options, then find the option to unhide hidden files, you will likely see the .Trashes, then a 501 folder (or something of the like), then your problem file.
How to fix it? The following worked for me:
1. Insert Windows XP installation CD
2. Restart the Mac
3. Hold down the Option key
4. When the Windows and Mac disk icons show up, hold down the C button on the keyboard, then a picture of a CD should pop up with the Windows name under it
5. Select the Windows CD, allow the Windows startup menu to load
6. Select the Install windows option
7. Then after clicking install windows (DO NOT click on the recovery panel option!), it will say that it found a version of Windows already on your C drive; select it and then select the option to repair it (I think for XP you need to hold down the R button, but be sure to read it to verify)
8. THen it will do a repair, say that it performed disk "maintenance" or something similar to your hard disk and say it needs to restart by pressing an F key then hitting enter
9. Allow it to restart, and voila, the file should magically disappear when you start it back in Mac OS X
This was startling to me because apparently with Windows installed, somehow, someway the corrupt nature of windows can still affect your Mac partition. Don't ask me how, but this solved my trash can problem and might help you out as well.