IBM think pad t42

Is the hard disk ATA or SATA?
Is the hard disk 2.5" or 1.8"?
What RPM does the disk run at?
Do you want a faster/slower disk?

Need more information.
 
okay, so find any laptop pata hard disk at 2.5", and it should work.

For an increase in battery, go for a 4800rpm disk.
For an increase in performance, go for a 7200rpm disk.