What OS are you running on it? If the 9x series, just hit cancel, and log in anyway. do a search for the *.pwl file and delete it, it will remove the password.
for other OS - such as NT, you might need to a boot disk, with support for reading a NTFS system - if the system was set up with NTFS. Sometimes those systems still go with FAT32, which will still allow it to be read with a fat32 bootdisk.
need to know what OS you have running on the system, what sort of system it is.