You might be able to repair the directory on the drive and get the "crashed" Mac running again, using Disk Utility.
You might be able to get your data off the drive via Firewire Target Disk mode, after buying the FireWire cable you need.
If the directory can't be sorted with Disk Utility and Target Disk Mode doesn't work at all, doesn't show the hard drive in the troubled machine, or can't find the files on it, your best bet will be to remove the drive, connect it to the good Mac through an external enclosure or USB adapter cable, and use data recovery software to salvage whatever data is intact from the drive.