I also own the Alesis Data Disk and have a huge library stored on that format. There is a company who makes a conversion from Data Disk To PC.
GO TO: http://www.midifile.com/
Giebler Enterprises Alesis Software Products
Featuring ADM - Alesis Diskette Manager
List/Print Datadisk Directory/Label
Copy Disk To/From HardDisk
Copy Datadisk Files To HardDisk
Copy File From HardDisk
Format Datadisk Diskettes
DataDisk Sequencer Conversion Software (ADDSMF)
Converts Type 0 or 1 Standard Midi Files (SMF) into Alesis DataDisk sequences.
Transfers all controllers, notes and tempo changes.
Does NOT require a midi interface for the IBM-PC.
Also converts Datadisk sequences into Type 0 Standard Midi Files.
Lists DataDisk and SMF sequences on the screen or printer.