For the limited space on the library palette the naming could consist of a easy to memorize part that is visible and some alphanumeric part that is not visible in Poser and that makes the file unique.

Something like "Some Shirt_2f3ee91635d7897a71209f02d01280e5.".
This should give plenty room for combinations until there's a better filesystem coming.
The maximum path lenght should be 256 characters for NTFS. With more then 244 it can cause errors however. Maybe the full hash with 32 characters is to long.
With an 8 character hash, like svdl suggested, there would still be ~281.5+e12 combinations for the hash alone, if restricting to 0-9 and a-f. Long before this number of files is reached the OS will have trouble and there is no such harddisk capacity available today anyways.