Unable to delete a file/folder
Tricky indeed, things to try


steps recommended by Apple (HT1526) but it seems you did most of them already
remove and recreate the whole trash folder: cd ~; rm -rf .Trash; mkdir .Trash; chmod 700 .Trash
delete by inode: cd .Trash; ls -i should give you the inode number; find . -inum INODE -exec rm {} \; deletes by inode number
hack rmi.c to compile under Mac OSX and use this to remove by inode directly (I haven't tested this)
boot into Recovery Mode (on Lion) or from DVD (Snow Leopard and earlier) and run fsck/volume repair
boot into single user mode (HT1492) and run fsck/volume repair