I need info off old hard drive

More information is required about the old computer, also what operating system? for instance is it capable of recognising the drive's full capacity and file format.
If you have a drive formatted in NTFS Win 98 won't be able to read it.
Is the drive SATA or PATA, is it installed on the same cable as the boot drive if PATA?
Another option is to get an external USB drive case to suit, or a powered USB adaptor.

More things to check.
1. You "Switched the setting to slave". This would imply it is an IDE (aka PATA) drive with a 40-pin data connector on a ribbon cable. Is that right? If it is a SATA drive, I'd worry about the term "slave".
2. Assuming it is IDE and set properly to Slave, is it on an IDE port / cable that already has another IDE drive set to be Master? If necessary, is it "Master with Slave Present"?
3. By any chance, is this set up with an optical drive as the IDE channel Master? sometimes opticals cannot function as a Master when the Slave is a hard drive.

You say that you have switched the drive to slave and installed in a second computer. One way to get info from this drive is
1. Switch the drive back to master.
2. Download and burn image of free sw like test disk http://www.cgsecurity.org/wiki/TestDisk on computer 1.
3. Boot computer 2 with this live CD. Connect an external hard drive to Computer 2.
4. Copy Data of from the internal hdd of computer 2 to external hdd of computer 2.



Test disk can read many file systems, so, you should be ok.