There is a feature in Poser 7 and 8 in General Preferences under the library tab called File Search.
Set it to None and Poser will not search at all (so all references need to have a correct path) or to Shallow where it will only look at the most logical places taking the existing path into account.
If set to Deep it will search everywhere (this is the default).
If you set it to Shallow it will find almost all files except when they do not exist, have been misspelled or are not in the correct location. On a very large library it always returns within a second, whereas a setting of Deep makes it search for a very very long time.

So set it to shallow and find out if this is acceptable